I've started collecting notes, updates, and errata related to the book on this page. This page may eventually grow to the have a more sophisticated multipage structure like that of the Learning Python 4E updates pages, but I'm adopting a simpler, informal policy here for now, partly because the book was just released, and partly because this book's more advanced audience will probably be more tolerant of the few inevitable typos along the way in a 1600-page book.
Below are the current and official lists of general notes and corrections for this edition of the book:
Only the last of these lists is true errata -- corrections, intended to be patched in future reprints. The first list represents an informal book "blog" of sorts. If you find an issue you wish to report, please post it on O'Reilly's errata list page for this book; I'm automatically emailed such posts.
Here are some of the main topics on this page:
I use this section to post general notes about the book, supplemental materials, and clarifications about book topics and examples. If any of these also deal with bugs or typos to be patched in the book itself, their formal fix is listed in the book corrections section. If this list ever had a specific ordering, it has been long lost to the ravages of time and edits; today, its items are loosely grouped by topic only -- latest notes, bonus examples, Python changes, example program updates, and miscellaneous.
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 below. 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.
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.
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) | write-up |
---|---|---|---|
2 | [Jan-10-11] | Closing temporary output files for HTML-only emails (patched in 1.2, and book) | write-up |
3 | [Aug-08-11] | Decoding and encoding non-ASCII attachment filenames (patched in 1.3, and book) | write-up |
4 | [Oct-01-11] | Improved sent-time display in list windows (patched in 1.3) | write-up |
5 | [Sep-29-11] | Delete and Save timing issue, rare bug (patched in 1.3) | write-up |
6 | [Jul-29-11] | Using authenticating SMTP servers for sends in mailconfig (patched in 1.3) | write-up |
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:
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.
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.
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.
(Update, July 2012: I've now verified that the "unofficial" PIL ports for Python 3.X described in the prior update do work correctly, at least on Windows under 3.2 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 the site http://www.lfd.uci.edu/~gohlke/pythonlibs/ runs fine for me in the book's PyPhoto program under Python 3.2.3 on a 64-bit Windows ultrabook laptop. Presumably, the 32 bit and Python 3.3 Windows installers as well as those for other platforms 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.)
(Update: a quick web search says that there are unofficial PIL installers for Python 3.2 and 3.3, including those here: http://www.lfd.uci.edu/~gohlke/pythonlibs/ , though I have yet to test their operation with book examples.)
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, Fredrik 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. Fredrik'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. ...
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.
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.
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 C:\SD-card-xfer-oct2711\Books\4E\PP4E\examples-official\1.3\unpacked\PP4E-Examples-1.3\changes\detailed-diffs\1.3\patched-files-13\i18n-filenames-tests Directory lists are identical Comparing contents Mail-saved-after-sent--OpenMeInGUI.txt matches
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):
c:\...\PP4E\System\Filetools>set PYTHONIOENCODING=utf-8 c:\...\PP4E\System\Filetools>diffall.py e: C:\SD-card-xfer-oct2711 > temp c:\...\PP4E\System\Filetools>notepad temp
Here is part of the temp output file, at the place where the prints failed before the environment setting:
-------------------- 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 C:\SD-card-xfer-oct2711\Books\4E\PP4E\examples-official\1.3\unpacked\PP4E-Examples-1.3\changes\detailed-diffs\1.3\patched-files-13\i18n-filenames-tests Directory lists are identical Comparing contents Mail-saved-after-sent--OpenMeInGUI.txt matches Поворот IMG_1412.txt matches 从~技~术~走~向~管~理.xls matches 金牌销售2天一夜实战训练.xls matches --------------------
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:
-------------------- 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 c:\SD-card-xfer-oct2711\Books\4E\PP4E\examples-official\1.3\unpacked\PP4E-Examples-1.3\changes\detailed-diffs\1.3\patched-files-13\i18n-filenames-tests Directory lists are identical Comparing contents Mail-saved-after-sent--OpenMeInGUI.txt matches --UNPRINTABLE FILE NAME-- b'\xd0\x9f\xd0\xbe\xd0\xb2\xd0\xbe\xd1\x80\xd0\xbe\xd1\x82 IMG_1412.txt' b'matches' --UNPRINTABLE FILE NAME-- b'\xe4\xbb\x8e~\xe6\x8a\x80~\xe6\x9c\xaf~\xe8\xb5\xb0~\xe5\x90\x91~\xe7\xae\xa1~\xe7\x90\x86.xls' b'matches' --UNPRINTABLE FILE NAME-- b'\xe9\x87\x91\xe7\x89\x8c\xe9\x94\x80\xe5\x94\xae2\xe5\xa4\xa9\xe4\xb8\x80\xe5\xa4\x9c\xe5\xae\x9e\xe6\x88\x98\xe8\xae\xad\xe7\xbb\x83.xls' b'matches' --------------------
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.
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 web site's directory.
I use this script for my training web site, 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 patttern 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.
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 (and in fact had to in 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 code -- use the "view source" option to view the form's HTML:
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.
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 of pylotto.py 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.
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.
I wrote this version to help resolve differences between iTunes collections on multiple machines that have fallen out of sycnc 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 files in the iTunes directory tree into 4 flat directories (playable, protected, irrelevant, and other), for each collection it's 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 merged the playable files directories with manual drag-and-drop operations, and also ran a simpler script, renamer.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 islolate 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 utility, for analysing 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:
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 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 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.
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.
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. Insted, these extensions work their magic by decoding raw binary bytes data to Unicode str text prior to parsing, using the ASCII encoding and passing "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, this 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 the 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 dilemas 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.
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, please see 3.2 release details and manuals.
While you're at the Learning Python site, see also its preview of mid-2012's expected Python 3.3.
As a cross-reference, be sure to see the Python 3.2 updates note above for changes in Python 3.2's email package which bear on the discussion in the section 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 at the note. I'd mark this as an insert for future reprints, but the book can't possibly track all future Python changes (especially with a new and incompatible email package under development); instead, this web page is meant to serve as a virtual and more easily updated appendix to the book.
(Update Oct-19-11: I couldn't resist fixing this one after all: see the release description above for more on version 1.3 of the examples package in which this fix appears. This fix was too large to add to the book itself.)
As is, 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 mail server only.
To fix: the time in the Date field of list windows should be shown in full, and 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' # explict 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):
>>> there = 'Thu, 29 Sep 2011 10:46:32 -0700' # pacific => gmt or local (eastern) >>> formatdate(mktime_tz(parsedate_tz(there))) 'Thu, 29 Sep 2011 17:46:32 -0000' >>> formatdate(mktime_tz(parsedate_tz(there)), localtime=True) 'Thu, 29 Sep 2011 13:46:32 -0400'
(Update Oct-19-11: I wound up patching this in version 1.3 of the examples package; 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. These fixes were too large to add to the book itself.)
The short story: though unlikely, it's possible that deletes may delete the wrong message if you request a new delete while one is already running. Don't do this, or read ahead to see how to fix this potential issue in code.
Here's the longer story. There is 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.
To avoid this potential entirely, don't run overlapping delete requests. To fix the code to avoid it in all cases, run 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: this was patched in release 1.3 of the examples package: see the release description above (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 mailtool package code it is also inherited by the less functional PyMailCGI webmail example in Chapter 16, but you may need to set your browser's encoding to UTF-8 to view the non-ASCII filenames embedded in the HTML reply stream.)
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 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.
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.
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!).
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:
return (filename, contype) return (self.decodeHeader(filename), contype) # aug 2011: decode fname
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/..."):
Content-Type: image/jpeg; name="=?KOI8-R?B?8M/Xz9LP1CBJTUdfMTQxMi5KUEc=?=" Content-Disposition: attachment; filename="=?KOI8-R?B?8M/Xz9LP1CBJTUdfMTQxMi5KUA==?= =?KOI8-R?B?Rw==?=" Content-Transfer-Encoding: base64with 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:
Content-Type: application/vnd.ms-excel; name="=?utf-8?B?6YeR54mM6ZSA5ZSuMuWkqeS4gOWknOWunuaImOiuree7gy54bHM=?=" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="=?utf-8?B?6YeR54mM6ZSA5ZSuMuWkqeS4gOWknOWunuaImOiuree7gy54bHM=?="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.
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 2011This 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.
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.
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 networkThis 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 587When 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 serverSee your ISP for more on your server settings, and the comments in mailconfig.py and the book for more on client configuration setings.
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, this 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.)
I recently spotted something unusual in Chapter 14's PyMaillGUI, 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 this 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 methods (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 I 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.
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 only happens 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 brower'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 an interested reader to address. As is, display of such emails employs a somewhat temporary scheme in lieu of an HTML-enabled text viewer, 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, impove as desired.
(Update Oct-19-11: per the release description above, this 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.)
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.
I've 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; probably 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.
Please Note: 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 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's 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 tring 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: I don't have time to explore it fully, or space to explain it here; for the full story, you'll have to trace through Python's 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 above, one of the otems 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.)
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:
Because PyEdit is a book example, written and provided in easily scriptable Python code, I'll leave applying these items as suggested exercise, along with anything else you might care to tweak. This is Python, after all.
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. 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, inprint(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: 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.
O'Reilly 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.
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 seem 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 webpage and its formal errata list for this book for the full list of typos collected and patched in reprints over time.
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.
server = smtplib.SMTP(self.smtpServerName) # this may fail too server = smtplib.SMTP(self.smtpServerName, timeout=15) # this may fail tooSimilarly, 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.
tmp = open(tempname, 'wb') # already encoded tmp.write(asbytes) webbrowser.open_new('file://' + tempname)to read as follows, adding the text that starts with the semicolon (I'm combining statements to avoid altering page breaks):
tmp = open(tempname, 'wb') # already encoded tmp.write(asbytes); tmp.close() # flush output now webbrowser.open_new('file://' + tempname)In the book's examples package, this code is located at line 209 in file PP4E\Internet\Email\PyMailGUI\ListWindows.py; it will be patched there too in a future examples package release (version 1.2, date TBD).
return (filename, contype) return (self.decodeHeader(filename), contype) # oct 2011: decode i18n fnamesSecond, 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 PP4E\Internet\Email\mailtools\mailSender.py):
# 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 2011Update 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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