This page collects notes, updates, and examples related to the book
Programming Python, 4th Edition (PP4E),
to serve as supplemental resources for this book's readers.
If this page's posts ever had a sequential ordering, it was either accidental
or abandoned long ago. Today, items here are best accessed randomly using the
topic groupings of the content lists below.
Note that there are only a few true errata (corrections) in the last list below,
all of which were fixed in early reprints. If you're looking for a complete
corrections list, or find a new issue you wish to report, please see the publisher's
errata page
for this book. That page automatically notifies me when new posts appear,
and hosts both book notes and answers to reader questions not duplicated here.
Related Resources
For more book resources, be sure to also see the following external pages,
some of which are newer than this page, and continue its mission:
[May-5-14]
New book-related example: Mergeall consists of a
script and GUI that synchronize directory trees, and can provide both an
incremental updates tool and a manual alternative to cloud storage.
Mergeall's main script reuses a number of directory-processing examples that appear in the
book's systems programming part. This program's coverage includes code and screenshots,
but grew too long for inline treatment here, and was moved off page.
As you'll find on that page, Mergeall eventually was ported to Mac OS too, and
packaged as both source code and standalone executables for Mac, Windows, and Linux.
It's a realistically scaled project that's too large to cover in the book, but
suggested as follow-up study for readers.
Update, 2017
For more book-related example code, see also the newer
Frigcal calendar GUI
example, which showcases Python's tkinter GUI library covered
extensively in the book, and the even newer
programs page, which leads to
upgraded versions of many of the book's major examples—most notably,
PyEdit,
PyMailGUI, and
PyGadgets.
[May-5-14]
I've recently begun running book examples on a Linux dual-boot system, under Fedora 20
and Gnome 3 (and later, Ubuntu). This is partly in response to the focus in Windows on
clouds, subscriptions, advertising, and devices that are proprietary and seem intentionally crippled,
but that's not what this note is about (see the related post).
So far, all the major GUI-based examples work well unchanged, with one minor exception: the script
used to launch PyMailGUI after selecting from one of N email accounts contains an unfortunately
nonportable and hardcoded Windows path. You may never encounter this; PyMailGUI can be run
directly too—and is by the book's demo launchers—and this script is in part
coded to work when PYTHONPATH has not been set to include the book's examples root. But to
fix the account-selector script so it works on Linux too, in this book examples tree file:
change the 2nd-from-last line from the first of the following to the second, in order
to pick up the underlying platform's path separator portably:
os.environ['PYTHONPATH'] = r'..\..\..\..\..' # hmm; generalize me
os.environ['PYTHONPATH'] = '..%s..%s..%s..%s..' % ((os.path.sep,) * 4) # hmm; generalize me
You may also want to change the last line from os.system('PyMailGui.py') to
something like os.system('python3 PyMailGui.py') in order to force 3.X execution
on Linux for the spawned PyMailGUI, but this depends on your system's links and
configuration (Python Windows launcher settings don't apply in any event—you'll
need to specialize this line's code per sys.platform if needed). There are undoubtedly
other Linux portability issues in smaller book examples, especially those in the Systems
section; more here as they surface. See also: tkinter Linux
portability notes elsewhere on this page.
Update, 2018
Subsequent to this post, the book's major book examples were also ported
to and run successfully on Mac OS.
For a sampling of some of the issues this platform poses, both GUI-related
and general, see the release notes of:
Each of the above programs is also available in source-code form that illustrates Mac
coding. Python and tkinter may be relatively portable, but some platform-specific
divergence is unavoidable. The Mac's richer GUI experience—including global toolbars,
slide-down dialogs, and app state—implies unique coding requirements.
Short story:
due to a temporary regression in Python's email package, you probably should not run
the book's PyMailGUI email client on Python 3.3.3. Instead, use any other
Python 3.X version—3.1 or 3.2; 3.3.0 through 3.3.2; 3.3.4 or later 3.3; or 3.4.0 or later 3.4.
The Regression in 3.3.3
[Mar-4-14]
In 3.3.3 only, Python's email package changed in a way that broke this book's
PyMailGUI. The break occurs when replying to or forwarding a message whose main body text contains
a non-ASCII character that was encoded per base64 or quoted-printable in the original message.
Such email messages worked fine in PyMailGUI from Pythons 3.1 through 3.3.2. In 3.3.3,
though, a simple slanted quote or emdash suffices to cause problems; when such characters
are present in the body text, PyMailGUI doesn't crash, but the message can't be sent,
and the GUI displays an error dialog with text:
Send failed:
<class 'UnicodeEncodeError'>
'utf-8' codec can't encode character '\udce2' in position 688:
surrogates not allowed
This makes no sense, given that surrogates are supposed to be employed
in the email package's new bytes API only—an API which
PyMailGUI predates, and does not use in any way (PyMailGUI decodes message
full-text to str text instead). The 3.3.3 email package must be
mutating the already-decoded body text, and inserting surrogate Unicode
escapes—something it absolutely should not do, and did not do until
the 3.3.3 point release.
Timing: because the error occurs on Send in the Message.set_payload() call following
the fix_text_required() workaround for an earlier email issue, a change in character-set
output encoding logic is the prime suspect. Before this point, the fetched
raw text of mails is correct (double-clicks show its original encoded form),
as is the result of mail parsing (View, Reply, and Fwd all display correctly
decoded text, including any non-ASCII characters). Both failing cases observed
were attempting to encode text per UTF-8 plus base64 on Send. In any event, the next
section makes this largely a moot point.
The Repair in 3.3.4
The good news is that this Python regression appears to have been present
in just one point release, and was fixed quickly. It has been observed in
3.3.3 only (plus an early 3.4 beta which inherited the issue temporarily).
It is not present in 3.3.2, and is fixed as of 3.3.4. Its
repair was also propagated to later 3.4 prereleases. Since the latest
official 3.3 and 3.4 downloads available at python.org—currently 3.3.4,
3.3.5rc2, and 3.4.0rc2—do not have the problem, its impact should be minimal.
PyMailGUI itself was coded for Pythons 3.1 and 3.2, current at book development
time, but is known to work well through 3.4.0, apart from this temporary
surrogates issue in 3.3.3. I use this program constantly, but only recently
discovered the issue when using a newer 3.3.3 install. It's less than
ideal for point releases to break working programs this way, of course, but
mistakes happen, and programs like PyMailGUI have to mind the bleeding edge
of Python releases more than most; book readers tend to prefer the latest
Python either way.
For examples of other PyMailGUI breakages caused by Python email package changes,
see the patch for item #3 on this page;
it's been a potential source of problems with each new Python release installed.
I've also observed some Windows line-break strangeness in recent email package versions
(text is sometimes saved as one long line), but this is to be investigated.
In the end, this makes for a reasonable lesson in itself: library dependencies
are an unavoidable aspect of real-world software development.
Footnote: You can verify the Python version that PyMailGUI is using by clicking
Write, entering the following program code in the Write window's main text area, and then
clicking its Tools -> Run Code menu option; this is a feature of the PyEdit component,
which runs the edited text as program code, and shows its output in the console window
where PyMailGUI was launched (don't try that in Outlook...):
import sys
print(sys.version)
Update, 2018
PyMailGUI eventually broke its dependencies on the
latest-and-greatest Python release by providing standalone executable
packages for each major desktop platform. These "frozen" executables
simplify installs and better integrate with platform GUI metaphors.
Perhaps more importantly, by bundling specific and verified versions
of Python and Tk, they grow immune to future changes in either. The
downside of such packages is extra build complexity beyond this update's
scope; see PyMailGUI's home page and
build folder for more details.
Short story: Tk, the library underlying the tkinter GUI module used in
book examples, does not currently support some Unicode characters. If unsupported characters
may crop up, programs need to replace these for display to avoid possibly uncaught exceptions.
PyMailGUI, PyEdit, and other book-related programs now do.
The Tk Unicode Issue
[Jan-16-14]
After using the threaded PyMailGUI on a daily basis for 8 years (more than 3 in its
latest 4th Edition form), a new issue cropped up when someone sent an email whose alternative
text part contained a Unicode character not supported by the underlying Tk GUI
library—character 🙊, which is Unicode codepoint U+1f64a
and u'\U0001F64A' in Pythonese, the "Speak-No-Evil Monkey"
character (no really; look it up).
The Tk GUI system can't handle character codes over
16 bits like this one (technically, outside the "BMP"), and PyMailGUI relies on Tk's
rendering prowess to do the right thing for Unicode, as described in the book; see pages 538-548.
As is, PyMailGUI reports the Tk error message in the console window and doesn't crash per se,
but the GUI is partly disabled, because this error is raised and uncaught in a thread-exit callback,
thus preventing a thread-busy lock from being released... which in turn disables future Loads, Views,
Deletes, and Quits (in fact, Task Manager may be required to close the GUI on Windows, and
similar elsewhere).
To do better, fetch this updated ViewWindows.py, and copy it
into your book example tree's PP4E\Internet\Email\PyMailGUI folder. It simply catches the Tk
library exception, displays a popup and stack trace, and continues, so that thread-busy locks are
released. Search for "1.5" in the file for more on the changes; the too-large Unicode character
also triggers a Tk exception in other places (e.g., viewing the text part later), but these are
already caught and reported with popups, and don't impact thread locks.
More PyMailGUI Ideas
From the semi-related-topics department: additional PyMailGUI changes to support POP over SSL,
SMTP over SSL/TLS, and POP servers that limit logins by time (thereby perhaps requiring a
single persistent login instead of one login per transaction) are in progress, but are also
suggested exercise. Accounts on outlook.com are one motivation for some of these mods. The first
two (SSL/TLS) are now supported in Python's libs, but not yet in PyMailGUI; see Python manuals
for usage details, and this related note on this page.
Update, 2016
For much more on the Tk Unicode limitation, see its later description
in the Frigcal docs.
That program confronts the same issue, in the context of calendars and events. This is most
egregious to people who abuse emojis (hey—you know who you are!).
Update, 2017
The Tk Unicode limitation in PyMailGUI—and the PyEdit component it uses—was eventually
addressed more globally in its standalone release available here. To fix,
all non-BMP Unicode characters are now replaced with the Unicode replacement character �
for display (until Tk supports more of Unicode, including emojis). There's more on the issue at large
in standalone PyEdit's user guide;
search for its "About emojis" notebox.
Update, 2018
Support for email servers that use or require SSL/TLS also eventually found its way
into PyMailGUI's standalone release; see its
change log and
mailconfig
files for details.
[Sep-15-13]
Per the description elsewhere on this page, a Python 3.3
standard library change broke some email address displays of non-ASCII names in
PyMailGUI, the largest example in the book.
In short, the Python 3.3 email package's formataddr utility function now
applies a new automatic MIME encoding for names, which it did not in the past—a curious and undocumented
incompatible change, which did not account for display-oriented use cases, and can break code that
worked well under Pythons 3.0 through 3.2 (including some in this book). Luckily, this is fairly
easy to repair.
To apply and use the patch for this Python change, simply fetch the following two files,
and copy them to the PP4E\Internet\Email\PyMailGui folder in your book examples tree,
per the more detailed instructions in the first of these:
py33patch.py—the patch to import, with self-test and docs
SharedNames.py—replacement for this file with required patch import
The first file updates the email package to be backward compatible for the duration
of the PyMailGUI program's run only. The second file, an existing part of PyMailGUI,
is simply augmented to import the first. The first file also has additional
documentation on the issue and its patch—see its comments for more details.
(And yes, this is a module-level example of what's called "monkey patching" today,
though applying a new label to an old technique doesn't necessarily make it any more
palatable...)
Update, Oct-15-13
There is a new 1.4 release of the book's examples package which incorporates
the small Python 3.3 patch described above.
Get the new examples release here,
and read about its 3.3 (and later) changes here.
Update, Nov-26-13
It has now been verified that this patch and the 1.4 examples
release also suffice
to make the book examples described here work under Python 3.4, per its beta releases.
Update, Oct-1-15
It's now also been verified that this patch and the 1.4 examples
release suffice
to make the book examples mentioned here work under Python 3.5, per its final 3.5.0 release.
Update, 2018
Naturally, this patch was also present in PyMailGUI's later
standalone release. This release
used Python 3.5 in 2017 and still does; later
3.Xs are not compelling enough to offset revalidation and
redistribution costs (despite the PR).
[Aug-22-13]
Because it is now officially an FAQ, this post includes the important bits
from a dialog with a reader who was having trouble running the web examples in the
preview chapter of the book. In short, on some machines you may need to
change the hardcoded port number used in this script to something other than
"80," and list it in the URL explicitly (and read ahead in the book itself to
the full coverage of this subject in later sections).
> > -----Original Message-----
> > To: lutz@rmi.net
> > Subject: Programming Python 4th Ed
> > Date: Wed, 21 Aug 2013 13:49:19 +0100
> >
> > Dear Sir
> >
> > Programming Python 4th Edition.
> > I'm stuck on page 53. Example 1-30 runs ok but I can't get example
> > 1-31 to reply. When I run the html script it lists the contents of
> > 1-31, How do I get it to execute 1-31?
> > I am using Python 3.3 on Windows 7.
>
>
> -----Original Message-----
> From: Mark Lutz [mailto:lutz@rmi.net]
> Sent: 21 August 2013 17:14
> Subject: Re: Programming Python 4th Ed
>
> There are too many things that can go wrong in the Web realm to offer advice
> based on your email (including but not limited to running the web server
> shown a page or two ahead). My advice is to read ahead to the server side
> scripting chapter of the book for the full story on the Web/CGI domain.
>
>
> -----Original Message-----
> To: 'Mark Lutz'
> Subject: RE: Programming Python 4th Ed
> Date: Thu, 22 Aug 2013 11:39:13 +0100
>
> Hi Mark
> Thanks for your prompt reply. I followed your advice to read further.
> When I run Example 1-32 Pg56 webserver.py I get the following output:-
>
> Python 3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 10:55:48) [MSC v.1600 32 bit (Intel)] on win32
> Type "copyright", "credits" or "license()" for more information.
> >>> ================================ RESTART================================
> >>>
> Traceback (most recent call last):
> File "C:\Users\...\Documents\AAAPROJECTS\COMPUTERSCIENCE\PYTHON\PROGPY33\C01\webserver.py", line 15, in
> srvrobj = HTTPServer(srvraddr, CGIHTTPRequestHandler)
> File "C:\Python33\lib\socketserver.py", line 430, in __init__
> self.server_bind()
> File "C:\Python33\lib\http\server.py", line 135, in server_bind
> socketserver.TCPServer.server_bind(self)
> File "C:\Python33\lib\socketserver.py", line 441, in server_bind
> self.socket.bind(self.server_address)
> OSError: [WinError 10013] An attempt was made to access a socket in a way forbidden by its access permissions
> >>>
>
> Could you please help me with "socket access permissions" as I am new to web
> programming. This is the reason I purchased your book to extend my Python
> Programming into web applications.
>
> I am running on my own Dell desktop as administrator using Windows 7
> Internet Explorer 10.
>
The webserver script works fine for me on Python 3.3 and Windows7.
Running the server in a Command Prompt window:
c:\PP4E\Examples\PP4E\Preview> py -3.3 webserver.py
127.0.0.1 - - [22/Aug/2013 09:04:08] code 404, message File not found
127.0.0.1 - - [22/Aug/2013 09:04:08] "GET /favicon.ico HTTP/1.1" 404 -
127.0.0.1 - - [22/Aug/2013 09:04:17] "POST /cgi-bin/cgi101.py HTTP/1.1" 200 -
127.0.0.1 - - [22/Aug/2013 09:04:17] command: C:\Python33\python.exe -u
c:\PP4E\Examples\PP4E\Preview\cgi-bin\cgi101.py ""
127.0.0.1 - - [22/Aug/2013 09:04:17] CGI script exited OK
And responding to this URL typed in a web browser window:
http://localhost/cgi101.html
Probably, you cannot run a server on port #80 (the script's default)
on your machine, because it is locked down by something else (e.g.,
virus software?). Try changing the port# in the webserver script,
and then name the port# in the URL explicitly:
port = 8080 # default http://localhost/, else use http://localhost:xxxx/
c:\PP4E\Examples\PP4E\Preview> py -3.3 webserver.py
http://localhost:8080/cgi101.html
Or, pass the port# in on the command line to the expanded version
of this script that appears later in the book, and run the examples
in that later section's directory:
c:\PP4E\Examples\PP4E\Internet\Web> py -3.3 webserver.py . 8080
webdir ".", port 8080
...server log...
http://localhost:8080/languages.html
This is all explained in detail later in the book in the
server-side scripting chapter. It's also mentioned in the
preview chapter you're reading; quoting from page 57:
"""
One pragmatic note here: you may need administrator privileges
in order to run a server on the script’s default port 80 on some
platforms: either find out how to run this way or try running on
a different port. To run this server on a different port, change
the port number in the script and name it explicitly in the URL
(e.g., http://localhost:8888/). We’ll learn more about this
convention later in this book.
"""
If changing port #s doesn't suffice, I'm afraid there's
nothing more I can offer; server setup is widely variable,
and may require some supplemental exploration.
Best wishes,
--Mark Lutz (http://learning-python.com, http://rmi.net/~lutz)
Short story: this section includes a now-dated summary of post-publication
changes to PyMailGUI, followed by updates on that program's later evolution.
Be sure to also see this section's updates ahead for more recent information.
PyMailGUI Post-Publication Changes Summary
[Oct-1-11]
After using the book's PyMailGUI email client for just over a year, I've collected
a list of additional enhancements beyond those already described in the book (see
the original enhancements list at the end of PyMailGUI's Chapter 14). I am the
entire testing department and user base for this program, so some issues have taken
longer to shake out than others. The following is a list of all these additional
PyMailGUI enhancements discovered and applied after the book was published, for
completeness; their write-ups are located elsewhere on this page:
1
Feb-01-11
Using POP and SMPT timeout parameters (patched in 1.2, and book)
Interestingly, two of these changes, #1 and #3, are also inherited by the less functional PyMailCGI
webmail example of Chapter 16, because they were applied in the common mailtools package.
There were a handful of additional changes made in the examples package and their book listings (e.g., a
focus fix in the PyEdit component used by PyMailGUI); see the
change log as well as the changes'
write-ups on this page for more details.
To sample the effect of changes #3 and #4 above, see the following PyMailGUI screenshots:
Mail view: a mail both sent from and viewed in PyMailGUI, with non-ASCII attachment filenames
Mail text: raw text of this mail (double-clicked), giving i18n filename encodings and date/time as sent
Mail list: the mail list window, showing converted date time for this mail relative to my time zone
Mail view: another mail sent and viewed in PyMailGUI, adding non-ASCII content and other headers
Mail text: raw text of this mail, giving MIME encodings for content, headers, and attachment names
The support for non-ASCII attachment filenames and local-relative time in these is new in the 1.3 example
package, but the rest is original behavior. See the book for more on PyMailGUI's i18n and Unicode
support in other headers and mail content.
Update: New Examples Release 1.3
[Oct-19-11]
I've posted a new release of the book examples package, version 1.3, which has patches
for all 6 of the PyMailGUI updates listed in this section above. The first two of these
were already patched in release 1.2, but the rest are new in 1.3. Get the change log and the complete
new examples zip file at O'Reilly's site, or
fetch just the files changed within it in this zip file. See the book
for details on running PyMailGUI in the examples package (via auto launchers, command lines, etc.).
I don't distribute this program standalone, partly because it uses many other files in the
book examples tree, and partly because the book is its documentation (but see the later update ahead).
One admin note: Some of the changes made in version 1.3 of the examples package are too large
to find their way into reprints of the book itself, but I recommend using the new version in
general, and studying the files changed to see what was involved; it's a fair example of code
maintenance in action. For changes too big to merge into the book, versions of the changed
source files which mirror the code in the book are retained in the examples package with
a "BOOK-" name prefix. For details, see the
change log which is also
file changes\CHANGES.txt in the examples package.
Update: Patch for Running on Python 3.3
[Sep-15-13]
There is a simple patch for an address-display issue introduced by a change in
Python 3.3's email package, that is included in version 1.4 of the examples package.
For details, see the bug, as well as its fix.
[2018]
PyMailGUI eventually was released as a standalone product (apart from the book) in 2017,
with numerous enhancements not noted here, and ports to Linux and Mac OS. You can read a summary
of all its post-publication changes here,
and trace its evolution at its home page and
user guide. The related
PyEdit program was similarly upgraded, ported, and packaged at the same
time; it's post-publication changes history is chronicled
here.
Book readers are encouraged to begin by studying the base versions of these programs in the
book, and move on to explore the new standalone versions' code later. The newer versions
are more polished for general use and portability, but retain the original versions' core ideas.
[Jan-4-12]
If a book example which uses the input() built-in seems to be failing,
and you are using Python 3.2.0 in a Windows console window, see
this post
on Learning Python 4E's update pages.
This built-in was apparently broken temporarily in 3.2.0 (3.2) in Windows
console mode, but has been fixed in later Python releases. The quickest fix
is to upgrade to 3.2.1 or later, or try a different environment; the book
examples work fine in all other Pythons and most other contexts such as IDLE.
Scripts in both books may be impacted by this regression.
[Jan-11-12]
Another cross-post from the Learning Python update pages about a Python change
which impacts examples in Programming Python too—see
this note
for details on Python 3.2's decision to drop support of str strings
for the "s" type code in struct.pack.
This impacts a variety of examples in this book. The simplest fix is to manually
encode str Unicode strings to bytes byte strings when passing to
struct.pack, per the referenced note. You can also run these examples in 3.1
or earlier if that's an option, though newer Pythons are generally better Pythons.
Short story: this section summarizes changes in Python 3.3, and
relates them to the book's content. As usual, code that aims to
illustrate the bleeding edge is generally among its first casualties.
An Overview of Python 3.3
[Oct-2012]
I've started testing the book's examples under Python 3.3,
the latest release which features:
A reduced memory footprint that is more in line with 2.X,
thanks mainly to its new variable-length string storage scheme,
and also to its attribute name-sharing system
A new namespace package model, where new-style packages
may span multiple directories and require no __init__.py file
New syntax for delegating to subgenerators (yield from ...),
suppressing exception context (raise ... from None), and
accepting 2.X's Unicode literals to ease migration (3.3 now treats
2.X's Unicode literal u'xxxx' the same as its normal str
literal 'xxxx', similar to the way 2.X treats 3.X's bytes-string literal
b'xxxx' the same as its normal str literal 'xxxx')
Reworked OS and IO exception hierarchies, which provide more inclusive
general superclasses, as well as new subclasses for common errors which
can obviate the need to inspect exception object attributes
A browser-based interface to PyDoc documentation, replacing its former
standalone GUI client search interface (use pydoc -b)
Changes to some longstanding standard library modules, including ftplib,
time, and email
New utility in the Windows installer which extends the system PATH
setting to include 3.3's directory as an install-time option to simplify
command lines
A new Windows launcher, which attempts to interpret Unix-style #!...
lines for dispatching Python scripts on Windows, and allows both #! lines
and new py command lines to select between Python 2.X and 3.X explicitly on
both a per-file and per-command basis
Plus more changes I won't list or repeat here. See my earlier
3.3 preview,
on the Learning Python update pages, as well as the official
3.3 What's New
document at python.org for additional details on 3.3 changes.
More on the New Windows Launcher: Off Page
Of these, the last 3.3 enhancement listed above will probably
have the broadest impact (in fact, it affects every Python
3.3+ user on Windows, which, for better or worse, is a huge audience),
and merits a few more words. Those
words have grown too large for this page, however, so I've
moved them to this separate article:
The very short story on the launcher is that it registers new
executables which are installed on your system path normally;
attempts to parse #! Unix-style lines at the top of scripts to
determine which version of Python run; and supports command-line
arguments that give Python version numbers. The net effect is
to better support multiple Pythons coexisting on the same machine,
by allowing Python version numbers to be specified on both a
per-file and per-command-line basis, and in both full and partial
form. It's quite a useful trick, though not without the pitfalls
described below. For much more on the launcher in general,
see the link above, or the new appendix on the subject in 2013's
Learning Python, 5th Edition.
Python 3.3's Impacts on Book Examples
PP4E's book examples were initially developed on 3.1, but tested
successfully on 3.2 alpha before publication. In general, most examples
tested so far appear to work well on 3.3 and as shown in the book. As
expected, though, the evolution in the 3.X line has impacted some behaviors.
Among the most notable 3.3 changes that affect book examples:
Standard library changes:
The standard library has undergone a number of changes which may affect this
book's examples, including changes to the ftplib and time modules.
See my earlier 3.3 preview
for details. The email package has also changed, but merits its own bullet here.
Email package changes:
As anticipated and described by the book, changes in Python's email package
have broken some aspects of the book's email examples, including the
larger PyMailGui program. Most of PyMailGui works fine as is under 3.3,
which is surprising given the scope of email changes. But non-ASCII (I18N)
email addresses in header lines which decoded properly in 3.0 through 3.2
no longer decode under 3.3.
For a graphical representation of this 3.3 regression, see this
screen shot—the PyMailGui window on the
left is the book's I18N saved-mail file open under 3.3, and the window on the
right is the same open in 3.2. The 3.3 version on the left fails to decode the
non-ASCII addresses which 3.2 handled, most likely reflecting an incompatible
API change. More details on a fix, as well as additional 3.3 email issues, as
they emerge.
Update, 9/2013: A patch for this 3.3 incompatibility is now available,
as described elsewhere on this page.
Windows launcher pitfalls:
This is probably the most prominent change in 3.3, as it has the
potential to impact everyone using Python on Windows,
and not just the book's examples. As for its general description,
though, the generic coverage of its pitfalls here has been moved
off-page to the last section of the launcher write-up. For the
full story, see
this page.
The short story in this department is that the new launcher:
Will now fail to run scripts having unrecognized #! Unix lines,
which causes a dozen book example files to fail in 3.3 (including
the top-level PyGadgets and PyDemos demo launcher scripts)
Will default to running Python 2.X for contexts that give no specific
Python version, which may cause many 3.X scripts to fail (including
files whose #! names just "python", as well as files with no
#! line at all—the normal case on Windows)
With respect to book examples, the first point requires changing
#!/bin/env to #!/usr/bin/env in a dozen examples files,
and the second point can be addressed by setting the launcher's default
to 3.X, via set PY_PYTHON=3 (or the equivalent in Control Panel).
The Python 3.3 installer also has an optional PATH extension
feature, which seems contradictory to the new launcher's goals,
but shouldn't cause scripts to fail in general.
As the off-page launcher write-up concludes, the new launcher is
a net Good Thing, but you need to be aware that it may break some
formerly valid scripts with #! lines, and may choose a default
version you don't expect which causes many scripts to fail initially.
More here on 3.3 in general as testing continues. You can also read about
earlier Python 3.2 changes here,
and later 3.4+ changes here.
Short story: PIL became the largely compatible Pillow, which is still
actively supported, and freely available at the standard PyPI website
here.
Fetch and install the Pillow drop-in replacement to run the book's image-related
PIL examples, per this section's updates. As of Tk 8.6, this install isn't
required if you just need to display PNG
images in tkinter GUIs.
The Issue
[Apr-21-12]
This book uses the PIL (Python Imaging Library) extension for some image-based examples,
both to render thumbnail images, and to display additional image file types in tkinter GUIs.
Because PIL was not yet ported to 3.X, the book employed a custom installer provided by
PIL's creator, and included this installer in its examples package as a temporary measure
pending an official 3.X port.
A reader wrote recently to note that the PIL installer in the book's examples package
works only under Python 3.1, and not for 3.2. I don't track PIL's progress, but it has
much more utility than the book leverages, and I suspect that this has held up the 3.X
port (naturally, this is a non-issue for 2.X readers, for which PIL installers are
available). Since this is a general issue which other readers have asked about too,
the relevant portion of my reply follows:
About a PIL installer for 3.2: an official 3.X PIL port has
yet to materialize; it was considered imminent two years ago.
The stop-gap installer I was given by PIL's creator and shipped
in the book examples package is an executable for 3.1 only,
which I unfortunately have no way to update.
I recommend contacting PIL's creator, F. Lundh, about
this, and/or browsing the archives of and posting your query
to PIL's email list to see what may be possible today.
PIL's creator's last known email address (two years ago):
(please search pythonware.com)
and the image-sig email list for PIL lives here:
http://mail.python.org/mailman/listinfo/image-sig
If you get a resolution on this and can spare the time, I'd
appreciate a copy on what you find; other readers have run
into the same issue. If I'm able to uncover anything myself,
I'll follow-up.
In the worst case, you can always install 3.1 alongside 3.2
to experiment with PIL examples, or take the examples' code
as demonstrative if not runnable.
The Interim
Update, May 2012
A web search turns up unofficial PIL installers for
Python 3.2 and 3.3, including those at
this site,
though I have yet to test their operation with book examples.
Update, July 2012
It's now been verified that the "unofficial" PIL ports for
Python 3.X described in the prior update do work correctly, at least on
Windows under Python 3.2 and 3.3 and for the PIL subset used by the book's
examples—tkinter image display, thumbnail generation, and resize operations.
Specifically:
The installer named PIL-1.1.7.win-amd64-py3.2.exe at
this site
runs the book's PyPhoto program fine under Python 3.2.3 on a
64-bit Windows ultrabook laptop.
The installer named PIL-fork-1.1.7.win-amd64-py3.3.exe, which follows
the newer naming scheme at the source site, was later shown to work with
Python 3.3.0 on this same machine as well.
Presumably, the 32-bit installers and those for other versions at this site also
work as expected. Thanks to both those who took time to port and post PIL, as well as
readers who asked me about this issue.
One nit on compatibility—to use Pillow instead of PIL, you must change any:
import Image
to this:
from PIL import Image
because of the way Pillow structures its namespaces. After this, Pillow works the same as
the former PIL (and as it's documented in the book), but bear in mind that additional
changes and deprecations have arisen over in Pillow time (e.g., Python 2.X is not supported
by its latest releases). For current status, read the summary of Pillow's morph
here,
and browse its full docs
here.
It's also worth noting that Tk 8.6 (included with python.org's
Python installers for Windows since 3.4, and currently bundled with its Mac OS installers) can display
PNG images in tkinter GUIs without any extensions, and all Tks can display
GIF and PPM/PPG images out of the box (more details
here and
here).
Pillow (f.k.a. PIL), however, is still required for both other image type displays,
and more advanced image operations (e.g., thumbnails, resizing).
[Oct-15-11]
I posted a note about pickling and bound methods on the clarifications page of the book
Learning Python 4th Edition which provides some additional background on how and why
bound methods cannot be pickled.
Since that note also pertains to the coverage of pickling in this book—in
Chapter 1's quick tour, Chapter 5's multiprocessing module section, and
Chapter 17's in-depth database material—I'm posting a cross reference to it
here too: read this
related note here.
Short story: Be sure to set your PYTHONIOENCODING environment
variable to support Unicode output on platforms that require this (and in Python
scripts that ignore this).
The Issue
[Oct-28-11]
On pages 279-282, the book discusses in substantial depth how
print calls can fail for some Unicode filenames in Python 3.X,
and uses a try statement to catch such failures in the tree walker
script on page 276. As described in the book, scripts should
generally print filenames with care in 3.X if those names might
ever be non-ASCII, by either catching print call exceptions or
changing the PYTHONIOENCODING environment variable to allow for
specific Unicode encodings in the standard streams. For simplicity,
though, some of the scripts in the book do not take this advice:
they simply print filenames blindly, and assume that you understand
the issue given the general description starting at page 279, and
will configure your environment if/as needed.
Filename Print Failures
As an illustrative example, I recently noticed a print failure
in the diffall.py directory comparison script on pages 311-313
after I added a few files with non-ASCII names to the examples
tree (tests for PyMailGUI enhancements described elsewhere on
this page). As is and without environment configurations, the book's
version of the script dies with an exception on Windows when printing
non-ASCII filenames, even if the output is redirected to a file (which
sometimes avoids such errors):
c:\...\PP4E\System\Filetools>diffall.py e: C:\SD-card-xfer-oct2711 > temp
Traceback (most recent call last):
File "C:\...\PP4E\System\Filetools\diffall.py", line 80, in <module>
comparetrees(dir1, dir2, diffs, True) # changes diffs in-place
File "C:\...\PP4E\System\Filetools\diffall.py", line 69, in comparetrees
comparetrees(path1, path2, diffs, verbose)
...
File "C:\...\PP4E\System\Filetools\diffall.py", line 56, in comparetrees
if verbose: print(name, 'matches')
File "C:\Python31\lib\encodings\cp1252.py", line 19, in encode
return codecs.charmap_encode(input,self.errors,encoding_table)[0]
UnicodeEncodeError: 'charmap' codec can't encode characters in position 0-6: character maps to <undefined>
The end of the temp output file reflects the location of the failure:
--------------------
Comparing e:Books\4E\PP4E\examples-official\1.3\unpacked\PP4E-Examples-1.3\changes\detailed-diffs\1.3\patched-files-13\i18n-filenames-tests to [...]
Directory lists are identical
Comparing contents
Mail-saved-after-sent--OpenMeInGUI.txt matches
Fix 1: Setting PYTHONIOENCODING
Now, as suggested in the book's footnote on page 282, this script works as
is without errors if you simply change your PYTHONIOENCODING environment
variable to UTF-8 Unicode encoding for the standard streams. No code
changes are needed, and the script winds up printing Unicode text to the
output file. On Windows (where you also set this once and for all via
the System icon in your Control Panel):
Alternatively, it might be a bit more robust and convenient in some scenarios
to catch the exception in the script itself and print as raw bytes, instead of
printing Unicode text that must be encodable per the print setting. A modified
version of this script that does this and works without environment setting
changes is available here: diffall-SAFE.py.
Here are the parts added and modified in diffall.py:
def tryprint(*args):
"""
Added Oct-27-11, post publication and post examples 1.3:
Don't fail with an exception for unprintable filenames;
See pages 279-282, and the similar tryprint on page 276;
Started failing for non-ASCII filenames in email test dirs;
In general, any filename printers in 3.X may require this,
unless PYTHONIOENCODING is set as needed (e.g., to utf-8);
"""
try:
print(*args) # filenames might fail to encode
except UnicodeEncodeError:
print('--UNPRINTABLE FILE NAME--', *(arg.encode() for arg in args))
def comparetrees(dir1, dir2, diffs, verbose=False):
...
if (not bytes1) and (not bytes2):
if verbose: tryprint(name, 'matches')
...
if bytes1 != bytes2:
diffs.append('files differ at %s - %s' % (path1, path2))
tryprint(name, 'DIFFERS')
...
for name in missed:
diffs.append('files missed at %s - %s: %s' % (dir1, dir2, name))
tryprint(name, 'DIFFERS')
if __name__ == '__main__':
...
for diff in diffs: tryprint('-', diff)
This changed script still makes some assumptions (it must be able
to encode the filename per the platform default, which is UTF-8 on
Windows) and may need further honing on some platforms. When run,
though, it avoids print failures explicitly; here's what it does
with non-ASCII filenames in the printed output in the temp file:
This works, but it many cases it might be simpler and will require
much less code to set your PYTHONIOENCODING as needed, rather than
trying to safeguard all your filename prints with try statements
on the off chance that they may someday fail. Even in the diffall.py
case, other modules that this script uses could potentially fail on
filename prints too, and may require additional error trapping code
unless we use the simpler and broader PYTHONIOENCODING scheme.
I'm not going to mark this for changing in reprints or new example
releases, partly because this is a general issue which is already
well documented in the book; partly because this is not the only
book example that takes a loose approach to printing filenames;
and mostly because such scripts will work without changes if you set
your PYTHONIOENCODING as needed. In other words, one can make a
very strong case that this is more an operational issue than a program
bug, and so does not merit a code change. As usual, if your scripts
fail on filename prints in Python 3.X, fix as prescribed.
Update: New Stream Defaults, ascii(), Mac OS
[2017]
As a postscript, the most recent Pythons have changed the default output
stream encodings to use UTF-8 on Windows, so you may not need to set your
PYTHONIOENCODING if you're using one of the latest releases.
See Python's What's New
documents for details.
Additionally, the built-in ascii(x) function can be used to escape non-ASCII text
for printing to streams if needed—an alternative to the to-bytes encode()
used above, and utilized on some platforms by the later
Mergeall system, which was the descendant
of the book's diffall and cpall scripts. See help(ascii) for details.
It's also worth noting that this issue seems most grievous on Windows. Mac OS,
for example, happily and naturally supports Unicode output in its Terminal app,
no environment changes required. But the world keeps using Windows anyhow...
cleansite is a book-related example originally posted here in 2010 and updated in 2014.
It recursively walks a website's links to locate unused files,
by parsing the HTML files accessible from one or more root pages, and noting the files of any type
they reference. Its goal is to help locate unused files that may be removed, while
leveraging multiple topics covered in the book.
Latest Version: Broader Usage Roles
[Feb-19-14]
The latest version of this script, 1.1, is available in this zipfile:
cleansite11.zip. The updated script,
cleansite.py, now handles parsing
of non-ASCII Unicode HTML files better; catches unused local files that have the same name as a
remote site's version named in a link; and is a bit more coherent on parameter selection.
The zipfile also has new example run logs, and updated versions of the book's downloadflat_modular.py
and uploadflat_modular.py FTP utility examples, updated to skip local and remote directories (now present
in their author's sites). Typical usage: run the download script to copy the site's top level; run cleansite to move
likely unused files to a subdirectory; manually inspect and adjust as needed (e.g., restore favicon.ico);
and run the upload script to clear the server site and upload the used files.
These scripts were used to purge old, unreferenced files from my websites—some now nearly
two decades old—by adding pages to ignore until old material was discarded as desired. For the
target site, cleansite caught 115 unused files among 317 total, and shaved 3G off its 10G total size.
You may need to augment this with multiple-file searches (see the Grep tool in the book's PyEdit GUI),
and this is still a bit user-specific, but serves its purpose for my use cases.
Original Version and Description
[Dec-28-10]
As a sort of reward for stumbling onto this page, I've uploaded an extra example
script here which would have appeared with the book's HTML parsing coverage
in Chapter 19, had this book project enjoyed unlimited time and space.
This script uses Python's HTML and URL parsing tools to try to isolate all
the unused files in a website's directory.
I use this script for my training website, as well as my book support site (the
latter after fixing some HTML errors that rendered the script inaccurate when
Python's strict HTML parser failed and caused some used files to be missed). This
script also includes code to delete the unused files from a remote site by FTP if
you wish to enable it (pending a resolution on the parser failures issue), and
includes suggestions for parsing with pattern matching instead of the HTML parser.
Download: The script itself lives here: cleansite.py.
To see what it does, read its docstring, and see two sample runs provided
in a zip file here: testruns.zip.
See also the newer, enhanced version of this script at the start of this section.
pylotto is a book-related script used to give away books to randomly selected students
in some of the live classes I teach (sorry, its lotteries are not open to the web at large!).
It ties together a number of the book's topics and techniques, and has been posted here in
both original and updated forms.
Latest Version: More Usage Modes
[Feb-22-11]
In light of security constraints in a recent class, I've completely rewritten
the pylotto script for worst-case scenarios. It can now select from both emails,
and a names file created manually or via web form submits, and can be run in both
console and remote CGI modes. In pathological cases, it can be run locally to
select from a local names file—the need for which was underscored by a recent class
somewhere in the wilds of California. I've also updated to port the single script to
work on both Python 3.X and 2.X, and to properly escape student names in the reply HTML.
Here's the new version's code—use the "view source" option to view the form's HTML:
pylotto.py, the main script, in a CGI directory in remote mode
pylotto.html, the sign-up form web page, on the server
Read the script's docstring for all the details. Among other things, it demonstrates
how to implement simple state retention in CGI scripts, using flat files and locks for
possibly concurrent updates to the players file. You can also view the
sign-up instructions files:
lotto-howto-email.txt and
lotto-howto-web.txt,
as well as a last-resort script which became a class exercise and
gave rise to (and is subsumed by) this new generalized
Pylotto: simple-pylotto.py.
The rest of this section describes the original, now defunct version, but also gives
the back story. The new version has the same goals, but supports web form and local file
sign-up modes in addition to emails.
Original Version and Description
[Jan-11-11]
Here's another supplemental example that might have appeared in the book,
if not for time and its conceptual dependencies. I wrote this script, pylotto,
in order to give away free books in some of the classes I teach. O'Reilly always
sends a batch of free copies to authors, and if I kept a dozen copies of every one
of the 12 Python books I've written, some of which are not exactly small, I'd
probably need a bigger house.
To enter the book lottery, students send an email message to the book's account,
with "PYLOTTO" in the subject line. At the end of the class, the script scans,
parses, and deletes these emails, and selects a set of their "From" addresses
at random as winners. It's not Vegas, but it's fair, and serves as a nice example
of practical Python programming that ties together a number of tools presented in
the book. This script also has a test mode that sends test emails, and an as-CGI
mode for running on a Web server if the training site doesn't allow POP email access
or SSH (many don't).
Download: Fetch the script here: pylotto-orig.py.
To see what it does, read its docstring, and see the text file that traces
its outputs in its various modes here: pylotto-orig-run.txt.
New: See also pylotto-orig-24.py, a version
modified to run remotely as a CGI script on a Python 2.4 web
server (that's the latest Python available on godaddy.com, as of January 2011!).
Naturally, I don't give away books in every class I teach (this basically
depends on how many freebies O'Reilly has given to me, and how willing I
am to lug around a big, giant book in my checked luggage). Even so, scripts
such as this one and others in the book which address real, practical needs
can go far to help illustrate Python applications in action once students or
readers have mastered Python language fundamentals. As stated in the book,
Python tends to become a sort of enabling technology for most people
who've learned to use it well.
flatten-itunes is a book-related example that copies all music files in a folder tree
to a single, flat folder for easier access and transfer, and puts some of the book's topics
to work on a realistic task. It's been released here in both initial and revised forms.
For reference, this section references the following code:
tagpix, a related tool, organizes photo folder trees
Latest Version: Resolving Disparate Collections
[Nov-5-11]
I've written a new and very different version of this script to be used
to isolate differences in iTunes collections on different laptops or
archives, rather than just flatten directories and detect protected files.
Grab the new 2.X/3.X version here: flatten-itunes-2.py.
Though it targets iTunes trees, it can be used to normalize (i.e., flatten)
any folder tree containing music files (e.g., unzipped Amazon MP3 downloads).
I wrote this version to help resolve differences between iTunes collections
on multiple machines that have fallen out of sync over time. It's easy to
get in this state if you buy songs on whatever laptop you have at the moment
and don't synchronize religiously (cloud storage addresses this in theory,
though not without potential downsides of its own). Because iTunes may
accumulate different files and directory structures on different machines,
it's nearly impossible to synchronize unless you normalize its files into
a simpler, uniform structure.
This new version addresses this by sorting all music files in an entire directory
tree into 4 flat directories (playable, protected, irrelevant, and other),
for each collection it is run against. This makes it simpler both to run later
comparisons to spot differences (e.g., using the book's
dirdiff.py or more in-depth
diffall.py scripts of Chapter 6), and to copy merged collections from device
to device. This version also retains all files in the tree; renames duplicates
with a numeric suffix; produces a richer
report; and was updated to run on both Python
2.X and 3.X. It's safe to run against an iTunes location just to experiment,
because it only copies files from there, and does not modify the iTunes tree
itself in any way.
After collecting files into flat directories with this script, I later merge
the playable files directories with manual drag-and-drop operations, and also
run a simpler script, rename-itunes.py,
on the result
to strip the leading track/disk numbers at the front of some filenames, making
it easier to compare and sort, and isolate more duplicates (e.g., "02 xxx.mp3"
and "xxx.mp3"). The end result is a single, flat directory of song files to
use on multiple devices.
Note: this is only an iTunes (or other music library) utility, for analyzing your collections'
content or moving your music files. It's not a player or iTunes replacement,
and although its result directories retain all iTunes music files, they may not
retain all iTunes information. For example, due to the way the script flattens
music directory trees, its result directories may lose some associations between
music files and their album artwork images, at least for images not embedded in
music files themselves (e.g., via ID3v2 frames for MP3 files). Writing a full
replacement for iTunes in Python (PyTunes?) would be an interesting
project, and others have already made progress along these lines—check out:
and lots more in the results of any web search for "Python MP3 player,"
"Python iTunes," or the like. It's a rich domain, but I've already
spent more time on this script than I meant to.
Original Version and Description
[Feb-3-11]
Here's something similarly practical, but a bit simpler than the prior two sections'
programs—a Python script which walks all the folders and subfolders in an iTunes
directory tree, to copy all music files in the tree to a single flat directory. I use
this to create a single directory of all my music on a memory stick, so it can be
used conveniently on the harddrive in a vehicle I drive. iTunes seems fond of nested
directories, and the player in the vehicle in question doesn't do well in their presence.
This example might have appeared in the larger systems examples chapter, if not for time, space,
and the fact that it's not too much different from tree-walkers already in that chapter.
Download: Fetch the script here: flatten-itunes.py.
To see what it does, read its code and docstring, and see the text file that traces
its outputs here: flatten-itunes.out.txt.
For another directory-walker media tool that similarly organizes media content spread across
folder trees, see also
tagpix, which extracts EXIF metadata tags
from photos with PIL, and is referenced elsewhere on this page.
Short story: this section deals with prominent changes in Python 3.2,
with a focus on email-processing tools that impact the book's examples.
An Overview of Python 3.2
[Dec-31-10]
As described in its Preface, this book was written under Python 3.1, and its major
examples were retested and verified to work under Python 3.2 alpha just before
publication. Because of that, this book is technically based on both 3.1 and 3.2,
though it addresses the entire 3.X line in general.
That said, you will find some discussion of 3.1 library issues in the book that
have changed or improved in the upcoming 3.2 version, which is due to be released
roughly two months after this book's release date (3.2 final is currently
scheduled for mid-February 2011). Some of the issues in 3.1's email
package which the book must workaround, for instance, have been improved or
repaired in 3.2.
In fact, many or most of the issues of the 3.1 email package described in Chapter
13 are fixed in 3.2. The email workarounds coded in that chapter still work under
3.2 (and were verified and even enhanced to do so before publication), but some
are no longer required with 3.2. Notably, the email package in 3.2 now supports
parsing the raw bytes returned by the SMTP module, thereby eliminating the
need for the partially heuristic and potentially error prone pre-parse decoding
to str that the book's 3.1-based examples must perform. The next section
explains how this works in 3.2.
email and bytes in 3.2: the Surrogates Replacement Trick
As a prominent example of email's improvements, 3.2's What's New document
states that the 3.2 email package's "new functions message_from_bytes()
and message_from_binary_file(), and new classes BytesFeedParser and
BytesParser allow binary message data to be parsed into model objects."
Interestingly, the 3.2 email parser still does not parse bytes internally.
Instead, these extensions work their magic by decoding raw binary bytes data to
Unicode str text prior to parsing, using the ASCII encoding and passing string
"surrogateescape" for the decoding call's errors flag.
In short, the surrogateescape error-replacement scheme translates undecodable bytes to
Unicode codepoint escape sequences, which allow the bytes' original values to be recovered when
the text is encoded back again to bytes by compatible software. When parsed message parts are
later fetched through the Message API, re-encoding back to binary form with the same errors
replacement scheme is expected to restore the original data. At least potentially, this
arguably clever trick could resolve the initial decode-to-str issue for parsing email messages
in Chapter 13.
On the downside, because this scheme assumes that message data is both decoded to Unicode text
and re-encoded to bytes later using the surrogateescape error handler for both steps,
this trick works for data passed through Python's APIs which follow this translation protocol, but
can fail for data which is not. Moreover, this scheme also assumes that any data mangled by
the surrogates-replacement step is not significant to the parser's analysis, as it might not
match expected characters in the stream—a non-issue for binary data or encoded text parts,
but potentially significant for some forms of full-message raw text (though non-ASCII bytes
are unlikely to mean much to a message parser in any form).
Also note that while this change may be a first step towards addressing the related
CGI uploads issue described in Chapters 15 and 16, that issue still exists in Python 3.2.
As described in the book, CGI uploads are somewhat broken in 3.X today because Python's CGI
module uses the email parser, but its uploaded data can be arbitrary combinations of both binary
data and text of a variety of Unicode encodings, with or without MIME encodings and content type
headers. Such data cannot be decoded to str in 3.1 as required by its email parser.
Unfortunately, the CGI module in Python 3.2 still uses the str-based email parsing API,
not the new bytes-based API, so this CGI uploads limitation appears to still be present
in 3.2. I verified that this is the case in 3.2 final: cgi does not use
email's new bytes parser interface, but still performs a pre-parse decoding from
bytes to str per UTF-8, which may fail for some data streams.
A resolution to this appears to await a future Python.
For email, though, 3.2's library fixes represent a significant improvement over 3.1: the
decode-to-str preparse issue for email, as well as other Chapter 13 email package workarounds,
may have been rendered superfluous in 3.2. On the other hand, the book's 3.1 workarounds code is
harmless under 3.2, and is representative of the sorts of dilemmas faced by real-world development
in general—a major theme of this book. Unless you're lucky enough to use the same version
of software for all time, change is probably an inevitable part of your job description too.
Other 3.2 Changes
For more on the Python 3.2 release, including its new __pycache__ subdirectory
bytecode storage model, please see
its note on this site
in the Learning Python 4E updates page (a book less impacted by 3.2, since 3.2
was supposed to change only libraries, not core language—and nearly succeeded).
Not covered in that note is the very late 3.2 addition of its
concurrent.futures library. This library, based upon a Java package, provides
yet another way to generalize the notion of multitasking with threads and processes,
in addition to the existing subprocess and multiprocessing modules which
are covered in this book. This new library is also a bit of a work in progress,
intended for future expansion. For more details, see 3.2 release details and
manuals. (Python 3.X's later evolution continued to explore parallel programming
but focused on asynchronous coroutines, which many viewed as narrow, complex,
and controversial; see this essay.)
While you're at the Learning Python site, see also its preview of mid-2012's expected
Python 3.3.
Update, Mar-2011
After additional research, it's now clear that the 3.2 email changes do indeed
bear specifically on the Chapter 13 discussion of Unicode and email that starts on page 926.
Most notably, the preparse decode from raw bytes to Unicode str
needed in 3.1 is no longer required (but is harmless) in 3.2, because the email
package can now parse bytes data directly, using the errors-replacement scheme described above.
I'd mark this as an insert for future reprints, but the book can't possibly track all future
Python changes as easily as this page (especially with a new and possibly incompatible
email package under development!).
Update, 2018
Be sure to also see the newer
Python Changes 2014+ page
for later Python changes not mentioned here. That page covers Pythons
3.4+, but its preamble also has links for Python changes that cropped up
between PP4E's publication and 2014 (post LP5E), including the later 3.3
coverage here.
Short story: the original version of PyMailGUI in the book didn't scale email
times to local (display) time, but this was added to the version in the book's examples
package early on using coding techniques described here.
The Issue
[Oct-1-11]
As originally coded, message-sent time is not displayed very usefully in PyMailGUI's list windows.
The GUI blindly displays the full, raw text of the Date header field. Worse, the time
portion of this header is truncated by the display such that the "+NNNN" field which
denotes what the sent time really is relative to GMT is not shown. The net effect is that
you can't tell in the GUI when a message was sent or which messages were sent before others
without looking at the raw text and deciphering the Date time string manually. The GUI
lists emails in order received at the POP mail server only.
The Fix
To fix, the time in the Date field of list windows should be shown in full, and be shown
relative to either the local time zone or GMT uniformly for all emails received. See
the Python email package for pointers and possible tools; this doesn't seem crucial enough
to detail the code fix here. As a hint, though, formatting dates for use in new mails can
be either relative to GMT or the local time zone:
>>> from email.utils import formatdate # in Python 3.2
>>> formatdate()
'Thu, 29 Sep 2011 17:27:53 -0000' # relative to gmt
>>> formatdate(localtime=True)
'Thu, 29 Sep 2011 13:27:55 -0400' # relative to local (us eastern, -4 hours)
>>> formatdate(usegmt=True)
'Thu, 29 Sep 2011 17:27:59 GMT' # explicit gmt relative for http
Applying the corresponding technique for adjusting a received date/time string
to the local time zone in PyMailGUI's code is officially delegated to suggested
exercise, but the following might help. To convert a GMT-based date/time string
to a date/time string in the local US Eastern time zone, try this (it's 5:45 PM
GMT and 1:45 PM locally):
>>> from email.utils import formatdate
>>> from email._parseaddr import parsedate_tz, mktime_tz
>>> now = formatdate() # gmt-based => local (eastern)
>>> now
'Thu, 29 Sep 2011 17:45:26 -0000'
>>> parsedate_tz(now) # time string => time tuple
(2011, 9, 29, 17, 45, 26, 0, 1, -1, 0)
>>> mktime_tz(parsedate_tz(now)) # time tuple => to utc timestamp
1317318326.0
>>> formatdate(mktime_tz(parsedate_tz(now))) # utc timestamp => time string
'Thu, 29 Sep 2011 17:45:26 -0000'
>>> formatdate(mktime_tz(parsedate_tz(now)), localtime=True)
'Thu, 29 Sep 2011 13:45:26 -0400'
Using this scheme to convert from local to GMT, or local to local
could proceed as follows:
>>> here = formatdate(localtime=True) # eastern => gmt or local (eastern)
>>> here
'Thu, 29 Sep 2011 13:45:47 -0400'
>>> formatdate(mktime_tz(parsedate_tz(here)))
'Thu, 29 Sep 2011 17:45:47 -0000'
>>> formatdate(mktime_tz(parsedate_tz(here)), localtime=True)
'Thu, 29 Sep 2011 13:45:47 -0400'
And finally, converting a date/time string from the US Pacific time zone
to either GMT or the local US Eastern time zone might be done this way
(it's now 10:46 AM Pacific, 5:46 PM GMT, and 1:46 Eastern/local):
Update, Oct-19-11
Because the patch was minor, I wound up fixing this in the examples package
after all: see the release description above for more on
version 1.3 of the book examples package in which this fix first appears.
As usual, the fix was propagated to all later PyMailGUIs.
The code edits were too large to add to the book itself, unfortunately,
so fetch the examples package for more details.
Short story: Though unlikely, it's possible that the original PyMailGUI's delete
(the GUI's Delete) may delete the wrong message if you request a new delete while one is
already running. Either don't do this; read on to see how to fix this potential issue in
code yourself; or get the latest book examples package or PyMailGUI release which
incorporated fixes for the issue long ago.
The Issue
[Sep-29-11]
PyMailGUI's initial version included an obscure timing issue related to delete operations.
As coded in the book, it's not impossible that a deletion thread's exit action may be
allowed to run and clear the delete-in-progress flag, before a new delete request has a
chance to check this flag. This can occur apparently because the new delete's
confirmation dialog popup releases control to the GUI event stream, which can then run
a prior delete's exit action from an after() timer callback event. Unfortunately, the
new delete issues the confirmation dialog before checking the delete-in-progress flag,
and after fetching message numbers to be deleted from the GUI.
The net result is that a new delete might overlap with one in progress, and incorrectly
delete the wrong POP message numbers made invalid in the GUI by the prior delete—a
scenario the book and code both explicitly state must be avoided. Note that the system
does go to great lengths to compare mail headers so as to ensure that each message being
deleted in the GUI matches the message being deleted on the server once deletions begin,
in case the server's inbox changes before a selected message is deleted (see method
deleteMessagesSafely in mailFetcher.py). That doesn't help in this
scenario, though, because the GUI client's mail list has been updated after selected
message numbers were fetched, such that the prior selections no longer match the GUI or the
server.
This behavior is timing dependent, rare, and can occur only if you issue a new delete
request while one is already in progress, and then only if you're unlucky enough to
have the prior request's exit action run exactly after the time you press Delete for
the new request and before you're able to click "OK" in the delete confirmation popup.
However, this is also a classic and even illustrative timing bug; it reflects both the
lack of broader testing for a book's examples, and a misconception of the confirmation
dialog's modality—the program assumed this dialog was truly modal (blocking),
such that all the code from the start of a new delete callback handler through its
delete-in-progress test ran atomically. This must not be case, as I've seen a few
incorrect mails deleted when running many deletes in parallel.
The Fix
To avoid this potential entirely, don't run overlapping delete requests.
Better still, fix the code to avoid it in all cases by running the delete-in-progress
test immediately in the delete callback handler, and before the confirmation dialog
is issued. Because the delete-in-progress test logic differs between the server and file
list windows, this can be done by either moving the confirmation dialog call into each
subclass's code, or adding a subclass-specific okay-to-delete method called from the
superclass delete callback code.
For more details, see onDeleteMail in the
ListWindow class on page 1074, as well as its two subclass's
doDelete methods on pages 1079 and 1083.
I may patch this in the examples package eventually, and in a book reprint if
possible; for now, consider it a maintenance exercise, as well as a lesson on both
the need for rigorous testing and the complexity of code that may overlap in time.
Update, Oct-19-11
Given its potential severity, I wound up patching and fixing this issue in version 1.3
of the book examples package. The fix, present in all later PyMailGUIs, prohibits
delete overlaps via the code changes described above; see the
release description above.
There appeared to also be a similar potential for timing issues for Saves due to their
file-selection dialog, which was also patched to check for blocking state before
the dialog instead of after, though this seemed much less likely or harmful.
Regrettably, these fixes were too large to add to the book itself.
Short story: this section describes a limitation in the original version of
PyMailGUI in the book, which was later lifted in both subsequent releases of the book's
examples package, and standalone PyMailGUI packages. Its resolution story told here,
though, is illustrative of both Unicode issues and code maintenance at large.
The Issue
[Aug-8-11]
After presenting the PyMailGUI client, Chapter 14 discusses a variety of
suggested improvements to this system. Among them, its Unicode enhancements
section on page 1123 mentions that the filenames of attached parts might
also be in i18N encoded form in some rare cases, and require the same MIME
and Unicode decoding steps that are already applied to other primary email headers
such as Subject, From, and To. In the book's PyMailGUI the
latter of these are properly decoded for display and encoded for sends, but
attachment filenames are currently not.
Encoded attachment filenames weren't present in the test cases used to
develop this version of PyMailGUI, so they received only a brief mention
in the improvements list. Moreover, some minor Unicode issues were
intentionally given limited attention, partly because this book's size
and time constraints limit its scope, but also because this edition
uses the Python 3.1 email package which has well-known Unicode issues
and limitations described in the text.
Lately, however, I've noticed that encoded filenames are becoming more common.
This doesn't seem like a great feature of email in general—Unicode filenames
that are encoded in a way not supported by the receiving platform's filesystem
won't work and would have to be renamed automatically (e.g., sending a Russian
or Chinese filename may fail when saved on an ASCII-only filesystem). Because
of the increasing prevalence of such emails, though, I want to elaborate on
ways to address them here.
GUI Workaround
As is, the only GUI-based way to handle parts with encoded filenames in the
client are to save the full enclosing email in a mail save file (list window:
select, and Save); edit the mail's text in its save file to rename the
attachment file name in its mail header line; and then reopen the mail from
its save file (list window: Open save file, select in popup file list window,
and View). This works, but obviously isn't a very user-friendly procedure.
Coding Fix
To do better, it might be simple to augment the partName method in
Chapter 13's MailParser class to route the raw filename fetched from
headers, to the decodeHeader header-text decoding method already
present in this class. This would apply the required email, MIME, and Unicode
decodings to such filenames, and yield a decoded Unicode filename string.
Since the result might use a character set that doesn't work on the underlying
platform's filesystem, though, this code would also need to try to encode it
per the local platform's filesystem encoding type, and come up with a different
name if the encode fails; it could follow the same naming pattern used for
attachments that don't have a filename- or name-header present ("partNNN.xxx").
For the adventurous, the MailParser class, used by PyMailGUI and other
clients, appears on page 976; its partName method on page 978;
and the required decodeHeader method on page 980. The platform's
filesystem encoding is described elsewhere in the book. It's too late to add
this enhancement in the book, of course, but changing this would make a nice
exercise in code maintenance (or see the next section, unless you want to
try this on your own!).
Update: Partial Fix Details
[Aug-15-11]
To help you get started, it appears that the first part of the coding fix,
decoding i18n filenames (but not also testing for their correctness on the
receiving platform), is simply a matter of changing the very last line of the
partName method in the MailParser class from the
first of the following to the second:
At least per minimal testing so far, this does the trick—Chinese and Russian
encoded attachment filenames are properly decoded, just like other encoded text
in primary email headers. These decoded filenames also happen to work unchanged
on the Windows operating system (per UTF-8) in their decoded forms, though they may
not work on some platforms, and their original i18n undecoded string forms always
fail as filenames on Windows too and generate error popups in the GUI.
For instance, a Russian email's JPEG image attachment whose i18n filename was given
in its part headers with a non-ASCII character set ("KOI8-R"), base64 translation
("B"), and the encoded text ("8M/..."):
with the patch is now correctly decoded to filename: Поворот IMG_1412.JPG.
The original encoded filename text in the headers does not work as is. Similarly,
a Chinese spam email attachment's headers using UTF-8, base64 encoded values:
now decodes to filename: 金牌销售2天一夜实战训练.xls (which will look right in this
web page if your browser understands UTF-8 text). With this patch, these decoded
filenames now appear correctly in the GUI's part buttons and its Parts list pop-up,
and when saved to files and opened in other applications. Non-encoded filenames
pass though the decoder unchanged as expected, so this should not break any cases
that worked previously.
Because this is a simple change that doesn't alter line numbers, and because encoded
filenames are becoming more common, I may mark this as a future reprints update, but
be sure to patch your code copy this way if it does not include the enhancement
and you start seeing encoded filenames in emails which you care to view.
TBD: Filesystem Limitations, Encoding for Sends Too?
Also keep in mind that the prior section's fix is partial: it still does not address
filenames which won't work on the underlying platform's file system and may need to be
renamed. Perhaps just as glaring, the fix handles decoding for display
of fetched emails only; there is no special logic for encoding non-ASCII attachment
filenames per i18n standards for sends—something which might have to be very
similarly addressed near the end of the MailSender class's addAttachments method
by passing filenames through that class's encodeHeader method, which modifies non-ASCII
text only. As is, on sends non-ASCII attachment filenames cause smtplib to raise ASCII encoding
exceptions for the full mail text in which the filename is embedded. Given that such encoding
is not supported by Python's email package automatically, the change may be as simple as
this—on page 964:
basename = os.path.basename(filename)
basename = self.encodeHeader(os.path.basename(filename)) # aug 2011
This should suffice: filenames that encode as ASCII are left intact and others
are encoded per the UTF-8 default, though it would ideally also apply the mailconfig
module's headersEncodeTo setting if present. But I'll leave this in the to-be-tested
column; I don't send such emails, and doing so seems a bit dubious in any event on the portability
grounds mentioned above. In other words, there is still plenty of room for
improvement. Enhance as desired.
The Standard Futurisms Caveat
Ideally, Python's email package would decode filename header contents
automatically and provide an alternative call for the rare cases when the raw
text is required, and encode filenames for sends automatically in non-ASCII cases.
Unfortunately, a future version of the email package may either decode
and encode filenames this way or not, so it's impossible to predict the optimal
resolution to this in future Pythons (as stated in the book, this was a primary
reason some email issues were not addressed as completely as they might have been).
As usual for software dependent on external libraries, be sure to watch for changes
on this front.
Update, Oct-19-11
This issue was patched and fixed in full for both sends and receives in release 1.3
of the book examples package, and is no longer present in any later PyMailGUIs.
See the release description which includes
screenshots of the fix,
and the formal patch description below.
This fix was small enough that it will appear in the book itself in a future reprint.
Note that because the fix was applied in common mailtools package code, it is
inherited by PyMailGUI, as well as the less functional PyMailCGI webmail
example in Chapter 16, though for the latter you may need to set your browser's encoding
to UTF-8 to view the non-ASCII filenames embedded in the HTML reply stream.
Short story: some ISP's email servers allow or require use of ports
with password-validated access and SSL/TLS secure transfers. Port numbers
are automatically supported in the book's PyMailGUI, and illustrated here;
user-configurable SSL/TLS support was added in the standalone release.
The Issue
[Jul-29-11]
As stated in the book, you may need to change your SMTP mail server
configurations to use the book's email clients to send email directly.
This is especially true when you try to send mail by SMTP on public
networks. Some of this is ISP-specific, but here are a few pointers.
This recently resurfaced for me because my email sends stopped working
after my broadband provider changed their network. In short,
they locked down the standard SMTP send port 25 in order to prevent spam,
but this prevented direct sends using the server configurations I had been
using. In the mailconfig.py file used by the PyMailGUI example,
my SMTP server configurations were originally the following—a simple
non-authenticating server at one of my third-party ISPs (Godaddy), which
worked fine on my home network and some others:
smtpuser = None # per your ISP, None = no login
smtppasswdfile = '' # if login, set to '' to be asked
smtpservername = 'smtpout.secureserver.net' # if port 25 open for SMTP on network
This no longer worked after the SMTP port lockdown. To send emails, I
had to change my SMTP server details to use an authenticating SMTP server
at another third-party ISP, running on a non-standard port number (this
server runs on EarthLink, which is different from my broadband provider):
smtpuser = 'lutz@rmi.net' # login, authenticate
smtppasswdfile = '' # ask for password in GUI
smtpservername = 'smtpauth.hosting.earthlink.net:587' # 3rd party ISP, port 587
When so configured, I have to login to my email account at this ISP on the
first email send in a session (PyMailGUI pops up a prompt for password
input), but Python's smtplib module automatically parses off and converses
over the custom SMTP port number included at the end of the server-name string.
This all just works in both PyMailGUI and smtplib, with no code changes required.
With these authenticated SMTP settings, email sends seem to work on many
more networks than before, and I avoid having to resort to webmail with
all its annoying advertising. As an alternative, I could have routed email
sends through the broadband provider's SMTP server directly, but this scheme
can sometimes be tagged as spam, and may require a direct connection to the
provider's network which may not always be possible:
smtpuser = None # per your ISP
smtppasswdfile = '' # set to '' to be asked
smtpservername = 'mail.mailmt.com' # your isp or local network's server
See your ISP for more on your server settings, and the comments in
mailconfig.py and the book for more on client configuration settings.
Postscript: I recently had to change servers yet again to use a broadband
provider account when EarthLink's SMTP server started timing out—the
following works in all contexts now for me, but your mileage will certainly
vary (and possibly, very often!):
smtpuser = 'myloginname' # nonblank=authenticated
smtppasswdfile = '' # ''=ask in GUI once
smtpservername = 'smtp.comcast.net:587'
Update, Oct-19-11
Per the release description above,
there is now a demo of the ideas presented here in release 1.3 (and later)
of the book examples package.
The changes were too large to add to the book itself.
Update, 2018
There is also more complete support for SSL/TLS secure email servers in PyMailGUI's
later standalone release. Such servers run on
dedicated ports, use password-based authentication, and are now commonly
required by many ISPs. See the latest PyMailGUI's
change log and
mailconfig
files for more information.
The sharp-eyed linear reader may also notice that this issue was touched
on as an unrelated idea in this note elsewhere on
this page (alas, long-running journals tend towards redundancy).
Short story: the original version of PyMailGUI in the book omitted a
file close call, which on some machines caused HTML viewers to misbehave.
This was repaired in version 1.2 of the book's examples, in the text of
the book itself, and in all later PyMailGUIs.
The Issue
[Jan-10-11]
I recently spotted something unusual in Chapter 14's PyMailGUI, in module
ListWindows.py, method PyMailCommon.contViewFmt (after about a year,
you get to be your own code reviewer). This method's latter part opens an HTML-only
email in a web browser after displaying its extracted plain text in a PyEdit frame,
and has worked well for my email ever since it was coded. To be robust and explicit,
though, it should probably run a tmp.close() after its tmp.write(asbytes),
to ensure that the output file's buffers are flushed to disk before the browser opens it.
This isn't a bug and the code works as is, but apparently only because of fortunate
timing: the browser started by the webbrowser module doesn't get around to
opening the temporary file until well after the PyMailGUI method exits—which deletes
its local variables, thereby reclaiming the temporary file object and automatically closing and
hence flushing it in the process. This works, but seems too implicit in retrospect, and
may not be the best coding pattern to emulate in any event. In general, you should run
an output file's close or flush method (or use the with statement
or unbuffered open modes) to flush output buffers to disk if you expect to be able to
read the file in the same program.
See Chapter 4 for much more on output file closes (including rules of thumb which
the book failed to heed in this context), especially pages 137-141 and 145. The prior
edition strung the open and write calls together:
open(tempname, 'w').write(content),
which, though still somewhat implicit, made the automatic close of the temporary file
on collection more apparent and immediate, and not as dependent on timing.
Later Findings: Some Machines Require Explicit Close
After seeing this issue manifest itself for very small HTML-only emails on a
much faster machine running a different operating system, I'm reclassifying this
as a correction to be patched in reprints and next example package version (1.2);
please see the
patch below.
When and where this problem occurs, an HTML-only email may open as a blank web
page, because its temporary file has not been flushed to disk. Oddly, on the
faster machine, the web browser somehow opens and reads the temporary file before
the GUI method has a chance to close it on exit. Moreover, this happens only for
very small emails (< 10K), suggesting a buffer size role. Adding an explicit
close() ensures proper behavior for all platforms and emails.
This issue is platform- and timing-specific; impacts just one minor aspect of a
very large program; and, even when it does, can always be worked around in the
user interface in three different ways—by pressing the web browser's
refresh/reload, by viewing the extracted plain-text in the GUI's main window,
and by clicking the sole HTML's part button in the main GUI window to open it
on demand. Still, it's annoying and simple enough to merit a patch.
For detail-minded readers, the faster machine with the incorrect behavior was a
multicore Windows Vista machine; the book test machine where the code works as is
was a single-core Atom Windows 7 machine (a beefy netbook). Since the Python
method in question returns immediately after this code, on Vista a web browser
apparently starts and opens a local web page faster than a Python method function
can exit. This may reflect differences in the implementations of start commands
in the two systems. I'd be surprised if this occurred on other platforms which
spawn processes to open browsers; on the other hand, unpredictable timing has a
way of being unpredictable.
As described in the book, there are other issues related handling of HTML-only
emails which I've left up to interested readers to address. As is,
in lieu of an HTML-enabled text viewer, display of such emails employs a somewhat
temporary scheme which was tested and used by just a single user on a single platform.
For example, its single temporary-file model means only the last such email
viewed is ever stored at any one point in time, regardless of how many are
opened. Such oddness does not occur for HTML parts opened on demand, because
their files are resaved and closed correctly in mailtools each time an open
is requested. As for much of this system, improve as desired.
Update, Oct-19-11
Per the release description above,
this issue was patched and fixed in release 1.2 of the examples package,
and the patch is present in all later PyMailGUI releases.
This patch was also applied in reprints of the book itself.
See the formal book patch description ahead.
Short story: PyMailGUI must use timeouts on server connections to avoid
hanging while waiting for interminable transfers. This support was added in
early versions of the book's examples package and in the book's text itself,
and is present in standalone PyMailGUI. This support has, however, been the
scene of multiple revisions and Python changes, and makes for a convoluted
and evolving story.
The Issue
[Feb-1-11]
The email-based code in Chapters 13 (and its clients in Chapters 14 and 16)
should probably pass timeout arguments to the poplib and smtplib
connection calls, to avoid waiting indefinitely. I've recently seen the book's PyMailGUI
desktop client get stuck waiting for a poplib connection call that never
returns, for example. This is rare, but without a timeout argument, your only
recourse is to wait seemingly forever, or kill and restart the GUI. See Python's
library manuals for more about passing timeout arguments in these modules.
Update: Timeouts Patch for Next Reprint
[Feb-22-11]
I've now added the timeout arguments as patches to be made in the next
reprint and examples package version (1.2): see the patch below.
This became a priority when I started seeing the email server at my ISP suddenly
failing to respond to connect requests on a very regular basis. This may have been
a temporary problem at the ISP, but killing and restarting the email
client's process manually was much more painful than patching to use timeouts for
server connections.
Update: More on Timeout Settings
[Mar-17-11]
If you wish to use PyMailGUI for real email work, you may
need to increase its email transfer timeout values to accommodate
slower Internet access speeds. As patched and shipped in the 1.2
examples package, both POP and SMTP timeouts are set to 20
seconds, which suffices in most cases. Especially for sending
large emails over slow connections or slow servers, though, a
higher SMTP timeout value such as 60 or more seconds may be required.
See the patch ahead for the location of
this value in the example code.
Discussion:
This is a surprisingly subtle issue, not covered in the book. POP and
SMTP timeout values were added after the book's publication to avoid
transfer threads hanging indefinitely—a scenario which may require
manually killing the email client's process in worst cases. For instance,
failure to contact the server on mail Load requests can render the GUI
largely inoperative (loads preclude most other operations, including Quit).
This is despite the fact that the load is run in a thread; the GUI itself
remains active, but cannot perform most server-based email processing
in this state.
Passing timeouts when connected to email servers avoids this by triggering
exceptions when server transactions hang, thereby terminating the server
transfer thread and producing an error pop-up in the GUI. However, Python's
library currently applies these timeouts naively to every server
interaction step performed on the socket created for an email transfer—not
just the initial connection calls, but also later data sends and receives.
This makes the timeout setting sensitive to the speeds of email servers, the
speed of your own Internet connection on the client, and message size in general.
This is true for both fetches and sends (POP and SMTP), though it is more
crucial for sends, which transfer a message's text all at once,
than for fetches, which read messages line by line.
Unfortunately, this seems a bit of a Catch-22—larger
timeout values allow larger mails to be transferred on slow connections,
but also mean that email transfer threads will be hung longer when servers
are truly inactive. Moreover, the timeouts can't generally be omitted
altogether, or the transfer threads may hang interminably—as mentioned,
in worst cases this may block other user operations in the GUI, and require
the email client's process to be killed manually when email servers become
unresponsive (this was the original motivation for the timeout patch).
Really, Python's email library modules should probably support different
timeout settings for different operations; one for all doesn't quite
make sense—sending a large email requires very different timeout
treatment than initial connection—but that's the API that exists today.
Although it's possible to implement more custom transfer timeouts manually
instead of relying on the existing library module support (e.g., add top-level
timer code around initial connect calls only), this would require too many
post-publication code changes, and would not suffice if later operations hang.
In principle, it's also possible to selectively enable and disable timeouts for
the socket embedded in and used by the smtplib object (e.g., disabling them
with server.sock.settimeout(None) for sends), but this is less than ideal from
a software perspective, as it makes smtplib module clients too dependent on the
module's internals: the module's API is intended to encapsulate and hide the
underlying socket object used. This would also fail to address servers which
become unresponsive during sends.
For sends, timeouts also trigger what looks like a bug
in Python 3.1's standard library—the mail send appears to fail after
the mail's text has been fully sent and while trying to read the server's
truncated reply to it, but only because the socket sendall() call 4 levels
down from the book's code seems to simply stop sending data and truncate
it when the timeout expires, without correctly raising an exception to
signal this error (on a Windows Vista client, talking to my ISP's server,
at least). This leads later to a confusing SMTPServerDisconnected
exception with the error text "Connection unexpectedly closed" reported in
the GUI and the console, even though the true cause was the earlier data
send's timeout. (This is complex, and there is neither time nor space
to explore it fully here; for full fidelity, see the Python source code
that raises this error, including its socket module's C code).
Increasing the timeout allows sendall() to finish sending
the data without truncation, and is required in some contexts in any event,
but it is also effectively a workaround for this erroneous behavior in
Python itself.
Summary:
Because of all this, in one of my own contexts I had to bump up the
SMTP timeout to 60 seconds to allow for sending a large email on a slow
network; otherwise, the send failed with an exception and an error pop-up.
Change likewise if and as needed for your context. Ideally, the mail
server timeouts would be configurable in the mailconfig module
instead of in executable source code files, but they were added after
publication when larger-scale changes in book code listings were no
longer possible (examples in books are ultimately meant to be demonstrative,
and don't enjoy, and may not even warrant, the level of update flexibility
common to software at large). Also ideally, Python's email library modules'
APIs would support different timeout settings for different operations as
mentioned above, but this will have to await a core developer's attention.
For better and worse, software dependencies make your software, well, dependent.
Update, Oct-19-11
Per the release description,
this was eventually patched and fixed in release 1.2 of the examples package,
as well as in reprints of the book itself. See the formal
patch description ahead for changes made;
timeout values are passed to POP and SMTP server objects at their connect calls.
Naturally, all later PyMailGUIs inherit the fix.
Update, 2018
This story changed yet again with 2015's Python 3.5.
In brief, timeouts in Python 3.5's socket module's sendall()
now apply to the entire call, not to each individual transfer it runs, and thus must
be set higher in general. Because the smtplib module uses this call,
this impacts email sends. For details, see the change descriptions for both
Python and
PyMailGUI.
The latter modified its timeouts settings in its standalone release
and made them user-configurable values (in its editable
mailconfig
files).
[Jan-9-11]
Chapter 11's PyEdit text editor is a large program with lots of functionality,
which I use nearly every day in one context or another. Besides text edits,
it's also a key component in the book's PyMailGUI email client. Still, like
most non-trivial user interfaces, there are plenty of ways its interaction might
be customized or improved, depending on its users' preferences. After using it
recently with the more critical eye afforded by the passage of time, five items
seem prime candidates for improvement; all are minor nits and not bugs,
but would be simple to improve, and might make nice coding exercises:
Respond to Enter in some dialogs
It might be nice if some of the nonmodal popup dialogs (Change, Grep, and
so on) would respond to Enter key presses too, instead of requiring button
clicks for activation as they do now. This should be easy to add, by
binding a keyboard event on these dialogs; see earlier in the GUI part's
chapters and examples for pointers on bind method events.
Show CWD in Grep dialog
In the new Grep dialog, a threaded and Unicode-aware file and directory
searcher, the root directory is preset to ".", meaning the current working
directory (CWD). In retrospect, this might be better set to the full
os.getcwd() path, as it's not always obvious where the program was
started ("." may not mean much if you don't know which program opened the
editor interface). The downside here is that the absolute path might be a
bit long for this dialog to display well. Of course, allowing a full
regular expression pattern for the search key would be nicer too, but
this potential upgrade is noted in the book already.
Disabling Unicode prompt popups
As shipped, the textConfig module configures PyEdit to always ask for a
Unicode encoding on Opens and Saves, when the encoding type is unknown
(and prefills with the platform default as a suggestion). It was shipped
this way because of PyEdit's role in Chapter 14's PyMailGUI, where the
Unicode encoding of some text items in email may be unknown; the best the
system can do is ask. Still, for most standalone use cases, it's a
bit of a bother to have to OK the Unicode encoding prompt dialog for every
Open and new Save, when the platform default will apply most (or all) of
the time. To disable the Unicode encoding prompt popups and apply the
platform's encoding default to your text files, simply change the values
of variables opensAskUser and savesAskUser from True to False
in file textConfig.py. See that file's comments and the book for
details, and this
related note on encoding defaults on standalone PyEdit's support page.
As coded, the Unicode prompt popups issued on Opens and Saves may cause
focus to be lost: you may need to click once in the text area before you
can start typing text or navigating with arrow keys, though not if you next
use scrollbars or view. This is a minor annoyance at worst, but seems to stem
from a buglet in the standard dialogs used for the popups (they should ideally
save and restore focus, as other standard dialogs do). It's also a non-issue
if you disable these Unicode popups altogether per the prior note's suggestion.
To force the issue for all cases, though, it's trivial to add a call to
self.text.focus() just after the dialog calls in the Open and Save callback
handler methods; see the Find and Goto dialog handlers for more hints. This
is assuming that focus is a desired feature, of course; in some cases, users
might proceed to scrollbars instead of arrow keys after an Open, and view
rather than edit.
(Feb-1-11: this was patched in book reprints and the book example package
release 1.2; see the patch details below.)
Clone might be better in the File menu
The Clone action, which creates a new, independent edit window, is currently
located in the Tools menu. To some, it might seem more typical and prominent
in the File menu instead. Moving it to File has a subtle downside, though:
because the File menu is removed (or disabled) when PyEdit is used in attached
component mode, Clone would be unavailable. For instance, in Chapter 14's
PyMailGUI email client, the PyEdit component has a Clone in Tools which currently
works fine—it creates a new PyEdit in a new Toplevel window, with the Frame-based
menus used in component mode. This can be useful for saving bits of text cut
from the mail message, and so on. Clone works the same in Chapter 11's PyView,
though its role there seems less compelling. Still, moving Clone implies tradeoffs.
Because PyEdit is a book example, written and provided in easily scriptable
Python code, except as noted I'll leave applying these items as suggested
exercises for readers, along with anything else you might care to tweak.
This is Python, after all.
Update, Oct-19-11
Per the release description above,
one of the items listed here (focus loss) was patched in release 1.2 of the examples package,
as well as in reprints of the book itself. See the formal patch
description ahead.
Update, Feb-2018
PyEdit has undergone major development in recent
years, which addressed usability issues and limitations far in excess of those listed
here. Its full set of post-publication changes is documented
here.
To get the latest PyEdit release with all the new enhancements, visit
its web page. It's available as standalone executables
for Mac, Windows, and Linux,
plus a source-code package that's suggested follow-up study (if far too large to
include in a book). While you're browsing, see also the standalone release of
PyMailGUI and other
programs, which have similarly evolved since their
book appearances.
[Feb-1-11]
A reader posted an errata report for this book on O'Reilly's site, which
claimed that a db.close() call is required to avoid file corruption
at the end of a Chapter 1 script that displays but does not update a shelve.
This report was about Example 1-19, but pertains to many others in the book.
Per the report, the shelve file triggers errors later, after it is updated
by the next script and then displayed again. Here is the post's text:
Type: Minor technical mistake
Description: There are no page numbers when using the Kindle version of
the text.
In the discussion of building dictionaries using classes, Example 1-19
(dump_db_classes.py) requires closing the db at the end of the script.
The final line of the code example should be:
db.close()
If the db is not closed, the subsequent updating (Example 1-20) and then
re-printing of the db (using dump_db_classes.py again) will fail, giving
an error code:
Traceback (most recent call last):
File "C:\Python31\dump_db_classes.py", line 6, in
print(key, '=>\n', db[key].name, db[key].pay)
File "C:\Python31\lib\shelve.py", line 113, in __getitem__
value = Unpickler(f).load()
EOFError
I have not been able to reproduce this error, and suspect that the poster's
kindle cut-and-paste simply dropped the close() call that appears at the end of
the update script in Example 1-20. In my testing, the scripts in question work
without error and as shown, both in Python 3.1 (using the "dumb" DBM file
interface default in 3.X), as well as in Python 2.7 (using the bundled bsddb
file interface default in 2.X). Moreover, these examples worked fine under
Python 2.5 for the prior edition of this book, and similar scripts have been
used successfully in earlier editions dating back to 1995. In general, shelves
should not require close() calls unless the shelve has been updated. By this
rule, a close() is not required in Example 1-19 (though it wouldn't hurt if
added); however, all shelve update scripts in the book do call
close() before exiting as required.
Because I can't reproduce this issue, I'm posting this as a clarification
instead of a correction for now, barring a more detailed reader report.
If you do see the same error, please email me with full context; the platform,
Python version, and underlying DBM interface in use may factor into behavior
too, and there are too many possible combinations for me to test exhaustively.
In the poster's defense, shelves are notoriously error-prone; it's not impossible
that file paths may have differed between scripts (the current working directory
can sometimes change unexpectedly in IDLE), or that a bad cut-and-paste
dropped the close() call in either the creation script of Example 1-18 or the
update script of Example 1-20.
Update Feb-2011
The reader who posted this note was later unable to reproduce
the error in question by repeating the steps which led to it, but believes
it existed initially. That may close the case, though there are too many
variables related to shelves to be certain.
[Jan-10-11]
O'Reilly Media (the book's publisher) recently asked me for written replies on a few questions
related to this book's scope, audience, and goals. Since this might help both current and
prospective readers understand the book in general, I've cut and paste the
replies on this page.
[Nov-15-15]
Recent development on the Frigcal
calendar GUI has underscored a number of portability issues and other usage notes
regarding Python's tkinter GUI library module used heavily in the book.
Linux Portability
In sum, for programs run on Linux:
An extra wait_visibility() is required for modal dialogs before grabbing focus with grab_set()
A transient() call is required for custom modal dialogs to prevent them from being covered
The iconphoto() call in Tk 8.5+ is better for window icons on Linux than iconbitmap()
Use withdraw() instead of iconify() to hide windows, if you wish to later deiconify()
The <map> and <unmap> events never fire on window restore/minimize on Linux
As the book notes, its many tkinter examples were developed and demonstrated on Windows 7,
and may require minor adjustments including the above for optimal use on Linux systems. The
vast majority of tkinter does work across platforms with no code changes, but top-level window
manager interfaces in particular are notoriously nonportable.
Other tkinter Notes
In addition to Linux use, the Frigcal program unearthed a number of noteworthy updates for
tkinter in general:
The <configure> event is also called for new locations (moves), not just resizes
There are more recent online resources for tkinter, including
this
The new uniform gridding mode is useful for tables (for row and column: weight=1, uniform='a')
Tk 8.6 (in Windows Python 3.4) now supports PNG image display, obviating PIL/Pillow in some use cases
For pointers on any of the above, see
Frigcal, and its release
history and
code,
and search the web for additional resources.
Update, Nov-2016
Per later porting, Mac OS X also poses a nontrivial set of Tk portability
issues of its own; see this note elsewhere on
this page for more details and Mac resource links.
[Nov-14-15]
Python's tkinter GUI library module, used extensively in the book and its examples, works
largely as expected, and well enough to power tools like email clients and calendars that I
use on a daily basis. Recently, though, I noticed that on rare occasions the book's PyMailGUI email
client GUI can appear to hang, and not update its display for email server transactions run in threads.
This most often manifests itself as non-modal message transfer "Busy" dialogs that are never erased.
After much puzzling, it was eventually determined that this occurs only when the system time has
been changed—for instance, on daylight savings time adjustments, or other automatic or manual
changes. And it turns out that this reflects a known issue in the Tcl/Tk library underlying
Python's tkinter, which underlies PyMailGUI. The issue may be known, but not widely so, and
underscores the tradeoffs inherent in software stack reliance.
In short, the widget.after() method arranges for an event to occur after a fixed
duration, by scheduling it to occur at an absolute time in the future, based upon the current
system time. If the system time changes, the event may never fire—or, more accurately, it will
be postponed until its absolute scheduled time is eventually reached with respect to the new
system time. To quote a Tcl/Tk document:
Tcl depends on the system time (converted to seconds from the start of the Unix
epoch) increasing fairly close to monotonically for the correct behaviour of a
number of things, but most particularly anything in the after command.
Internally, after computes the absolute time that an event should happen and
only triggers things once that time is reached, so that things being triggered
early (which can happen because of various OS events) don't cause problems.
If you set the system time back a long way, Tcl will wait until the absolute
time is reached anyway, which will look a lot like a hang.
In PyMailGUI, this looks like a hang, but it's not. Really, the thread-queue checker's
widget.after() is postponed indefinitely, such that finished and queued email
server transactions are never noticed in the main GUI thread. The GUI itself remains active,
and the email and thread logic works as planned; the widget.after() timer
loop simply stalls due to the clock change, and no longer pops and dispatches callbacks that
have been added to the thread queue. Hence, the email operations succeed, but the GUI
isn't updated.
There is no known fix to this. If your PyMailGUI appears to not be processing email
transactions, simply restore your system clock, or restart PyMailGUI. There is a good
chance that a future Tcl/Tk release may address this by using a "monotonic" clock:
one that has no reference point but can never go backwards, and so isn't susceptible
to such change. In fact, Python now has such an interface—see time.monotonic(),
new in 3.3 and always available as of 3.5. A Tcl/Tk fix on this front would be inherited by
both tkinter and PyMailGUI, as well as all other GUIs with timer loops based on after().
[Nov-14-15]
I've gotten numerous emails from readers who have trouble using some of the
book's FTP and email Internet examples as coded in the book. In short, you
must change the configuration settings in these scripts to use your own FTP
server and email accounts. The CGI server-side scripting examples require no
such change, as they run entirely locally—including their web server.
I thought this was stated clearly in the book, but it's come up often enough
to warrant pasting a reader query and reply on the subject here.
> -----Original Message-----
> From: ....
> To: lutz@learning-python.com
> Subject: chapter 13 example
> Date: Fri, 13 Nov 2015 16:35:41 -0800
>
> I have a question on the getone.py example. When I run it the ftp.rmi.
> net doesn't seem to work. I see you have changed to the learning python
> site but when I use the new site the same problem occurs with the
> password input. I've tried (), anonymous, and my email address. ? what
> to do to connect.
> I've been reading your books now for about 13mths. I'm
> approaching this like learning a foreign language and enjoying it. I
> haven't moved to 3.5 as the 3.4 v seems to work well. Thanks for any
> help you can give.
>
Thanks for your note. Unfortunately, I do not maintain an
FTP account for use by readers of the book. With many thousands
of readers around the world, this would be too large a task and
security risk. Instead, the assumption is that you will replace
the site and login details with those of servers to which you
have access, if you wish to run such code live.
This also applies to the later email (and other) examples: please
change configuration files to use your own account, as described
in the book. The server-side examples are more immune to this,
as they use a Python-coded server running locally on your machine.
Best wishes on Python and the book,
--Mark Lutz, http://learning-python.com
In a book this large there are bound to be a significant number of typos,
and I don't plan on listing them all here. Instead, this section will
collect those typos that at latest update time seemed most grievous to me on purely
subjective grounds (of course, your subjective grounds may vary). The items here
reflect patches made to the book itself in reprints; code patches too large
for the book appear in the example package only. See
O'Reilly's web page
and its formal
errata list
for this book for the full list of typos collected and patched in reprints over time.
Page xxviii, line 3 from page top: two typos in same sentence
This text's
"larger and more compete example" should be
"larger and more complete examples".
Page 678 in Chapter 11, line 3 of last paragraph on page, figure description off
The text misstates Figure 11-4's content here: it does not show a Clone
window (the original version of this screenshot did, but was retaken very
late in the project to show Grep dialogs with different Unicode encodings).
To fix, change this line's
"a window and its clone" to read
"a main window".
Page 702 and 704, PyEdit: add text.focus() calls after askstring() Unicode popups
For convenience, and per the detailed description above, we should
add a call to reset focus back to the text widget after the Unicode encoding prompt popups which
may be issued on Open and Save/SaveAs requests (depending on textConfig settings). As is,
the code works, but requires the user to click in the text area if they wish to resume
editing it immediately after the Unicode popup is dismissed; this standard popup itself
should probably restore focus, but does not. To fix, add focus calls in two places.
First, on page 702, at code line 21 at roughly mid page, change:
if askuser:
try:
text = open(file, 'r', encoding=askuser).read()
to the following, adding the new first line (the rest of this code is unchanged):
self.text.focus() # else must click
if askuser:
try:
text = open(file, 'r', encoding=askuser).read()
Second, on page 704, at code line 8 near top of page, similarly change:
if askuser:
try:
text.encode(askuser)
to the following, again just adding the new first line:
self.text.focus() # else must click
if askuser:
try:
text.encode(askuser)
Reprints: please let me know if there is not enough space for the inserts;
I'd rather avoid altering page breaks in the process. This patch will also
be applied to future versions of the book's examples package; in the
package, the code in question is in file
PP4E\Gui\TextEditor\textEditor.py, at lines 298 and 393.
Update, Feb-24-11
Patched in version 1.2 of the book examples package (PP4E-Examples-1.2.zip).
server = smtplib.SMTP(self.smtpServerName) # this may fail too
server = smtplib.SMTP(self.smtpServerName, timeout=15) # this may fail too
Similarly, change code line 4 on page 970 from the first of the following to the second:
server = poplib.POP3(self.popServer)
server = poplib.POP3(self.popServer, timeout=15)
In the book examples package, these changes would be applied to
line 153 of mailSender.py, and line 34 of file mailFetcher.py,
both of which reside in directory PP4E\Internet\Email\mailtools.
They'll be patched in a future examples package version.
Update, Feb-24-11
Patched in version 1.2 of the book examples package
(PP4E-Examples-1.2.zip). I made the timeout 20 seconds in the examples package, to allow
for slower email servers; 15 is more than enough to detect a problem with mine, but tweak
this as desired.
Update, Mar-17-11
Because timeout settings are used for every server
interaction step, you may need to use a bigger timeout value (e.g., 60 or more seconds)
in some contexts, especially when sending a large email over a slow client-side connection.
See the update at the detailed description above for more on this.
Page 1072, code line 10 from top of page, PyMailGUI: add a close() for HTML mail files
For portability, and per the detailed description above, we
should add an explicit close() call to flush the temporary file of an HTML-only email
before starting a web browser to view it, so that this code works in all contexts.
As is, it works on the test platform used for the book, and likely works on
most others, because the method in question exits and thus reclaims, closes,
and flushes the file before the spawned web browser gets around to reading it.
However, this is timing and platform dependent, and may fail on some machines
that start browsers more quickly; it's been seen to fail on a fast Vista machine.
To fix in the book, change the middle line of the following three current code
lines:
In the book's examples package, this code is located at line 209 in file
ListWindows.py at PP4E\Internet\Email\PyMailGUI;
it will be patched there too in a future examples package release (version 1.2, date TBD).
Update, Feb-24-11
Patched in version 1.2 of the book examples package (PP4E-Examples-1.2.zip).
Page 1226, two filename typos in same sidebar
This will probably be obvious to most readers who inspect the external example files
referenced here, but in this sidebar:
"test-cgiu-uploads-bug*" should read
"test-cgi-uploads-bug*",
and the bullet item text
"test-cgi-uploads-bug.html/py saves the input stream" should read
"test-cgi-uploads-bug2.html/py saves the input stream".
Page 1555, top of page, quotes are misplaced in heading line
A typo inherited from the prior edition: the quotes and question mark
in the heading line at the very top of this page are slightly off. Change the
heading line:
So What's "Python: The Sequel"? to read as:
"So What's Python?": The Sequel. Quotes are angled in the original
and revision. This header refers back to the
sidebar in the Preface titled "So What's Python?". Arguably trivial,
as this sidebar was 1500 pages (and perhaps a few months) ago by this
point in the book, but it would be better to get this right. This header
was broken by a copyedit change on the prior edition, and fell through the
cracks on this one.
Pages 978 and 964, encode and decode i18n attachment filenames for display, save, send
Per the detailed description above, the following two changes will
support both receipt and send of encoded i18n attachment filenames, assuming that such non-ASCII
filenames are valid on the underlying platform (Windows is very liberal in this regard).
First, on page 978, change the very last line of the partName method def statement
from the first of these to the second (this is mid page at code line 26, in file
mailParser.py at PP4E\Internet\Email\mailtools):
Second, on page 964, change the 5th and 4th last lines of the addAttachments method def
statement from the first of these to the second
(this is mid page line -22, in file
mailSender.py at PP4E\Internet\Email\mailtools):
# set filename and attach to container
basename = os.path.basename(filename)
# set filename (ascii or utf8/mime encoded) and attach to container
basename = self.encodeHeader(os.path.basename(filename)) # oct 2011
Update, Oct-19-11
Patched in version 1.3 of the book examples package (PP4E-Examples-1.3.zip),
and scheduled to be applied in future reprints of the book itself.
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