11. GUI Programming

What makes Python good at GUIs?

♦ Rapid turnaround… easy to experiment

♦ Very high-level… fast to code GUIs

♦ Object-oriented… code reusability

♦ Dynamic reloading… changes without stopping

Python GUI options

♦ Tkinter: simple code for simple GUIs

● Python’s OO interface to the portable Tk API

● Part of Python, lightweight, well documented, robust

● Meshes well with a scripting language: from Tcl

● Runs with native look-and-feel on X, MS-Windows, Macs

● Structure: [tT]kinter + Tk lib + (X, Windows, Mac libs)

● A de-facto standard: Tk used by Python, Perl, and TCL

● An open source system, supported/used by many

♦ wxPython: complex code for richer GUIs

● Second most popular GUI API for Python (or is it PyQt?)

● Portable GUI class library written in C++ (X, Windows, Mac)

● Wraps a C++ API: wxWidgets + wxPython

● Rich widget set: trees, html viewers, notebooks

● Tends to be more complex: C++ API (wx) verses scripting API (Tk)

● Was less documented, but wxPython book in 2006

● GUI builders: BoaConstructor, wxDesigner

● Tkinter + PMW package roughly as rich as wxPython?

♦ PyQt, PyGTK: on the order of wxPython

● From KDE & Gnome Linux libraries, but now portable

● PyQt third most popular GUI API for Python (?)

● PyQt: works on Sharp Zaurus PDAs, open source book

● PyQt: was not completely open source (but is today)

● Qt GUI builders: BlackAdder, QT Designer

● Example use case: free Calibre ebook viewer

♦ Jython (a.k.a. Jpython, originally)

● Access to Java GUI APIs: AWT, Swing, etc.

♦ IronPython .NET/Mono port

● .NET may provide GUI tools usable in Python scripts

♦ Rich Internet Applications (RIAs)

● Blurs line between “desktop” and web clients/GUIs

● Run in a web browser, javascript/ajax to be dynamic

● Gains browser portability at cost in software stack depth

● Pyjamas—now Pyjs (Py=>JS compiler, GWT toolkit), Silverlight (IronPython), Flex, etc.

♦ PyWin32 (former known as win32all)

● MFC integration for Python on Windows (only)

♦ PythonCard

● API + drag-and-drop builder on top of wxPython

♦ Dabo

● 3-tier application builder with GUI, Dbase, logic

♦ Anygui

● Portable API implemented on top of Tk, wx, Qt

See: Extras\Code\Gui\wxPython\wxPython.doc on CD for Tkinter, wxPython comparisons

The Tkinter ‘hello world’ program

♦ Widgets: class instances

♦ Options: keyword arguments

♦ [tT]kinter exports classes and constants

♦ Widgets must be packed (or gridded, placed)

♦ ‘mainloop’ shows widgets, catches events

♦ 3.X: ‘Tkinter’→‘tkinter’, supplemental modules renamed

file: gui1.py

from Tkinter import * # get widget classes

Label(text="Hello GUI world!").pack() # make a label

mainloop() # show, catch events

% python gui1.py

Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: gui1

Adding buttons, frames, and callbacks

♦ Frames are widget containers

♦ Widgets attach to sides of a parent

♦ Event handlers are any callable object

♦ Button handlers are registered as ‘command’ options

file: gui2.py

from Tkinter import * # get widgets

def callback(): # define handler

print 'hello stdout world...'

top = Frame() # make a container

top.pack()

Label(top, text="Hello callback world").pack(side=TOP)

Button(top, text="press me",

command=callback).pack(side=BOTTOM)

top.mainloop()

% python gui2.py

hello stdout world...

Example: a live GUI demo

Getting input from a user

♦ Entry is a one-line input field

♦ lambda defers call to add an input argument

♦ showinfo is one of a set of common dialog calls

♦ Tk main window & Toplevel popups have icon, title

♦ + multi-line text, menus, radio/check buttons, dialogs,…

file: gui3.py

from Tkinter import *

from tkMessageBox import showinfo

def reply(name):

showinfo(title='Reply', message='Hello %s!' % name)

top = Tk()

top.title('Echo')

top.iconbitmap('py-blue-trans-out.ico')

Label(top, text="Enter your name:").pack(side=TOP)

ent = Entry(top)

ent.pack(side=TOP)

btn = Button(top, text="Submit",

command=(lambda: reply(ent.get())))

btn.pack(side=LEFT)

top.mainloop()

Assorted [tT]kinter details

Other event interfaces

● widget.bind(“<B1-Motion>”, func) [CD bind.py]

● widget.after(msecs, func)

● slider/widget linkage, data stream conditions

GUI construction

● “What you build is what you get”

● Layout = build order + pack options

● Each Toplevel instance is a window

● Default Toplevel window if no parent

● Widgets nest in Frames, Frames nest in other Frames

● Object trees: Tkinter cross-links parents to children

“Decreasing Cavity Model”

► pack gives widget entire side

► widgets packed later get side of what’s left

► grid, place: alternative geometry managers

OOP: Building GUIs by subclassing frames

♦ Organization framework: namespace, inheritance

♦ Methods attach widgets to ‘self’

♦ Callbacks are bound methods of ‘self’

file: hello.py

#!/usr/local/bin/python

from Tkinter import * # get widgets

class Hello(Frame): # container subclass

def __init__(self, parent=None):

Frame.__init__(self, parent) # superclass init

self.pack()

self.make_widgets() # attach to self

def make_widgets(self):

widget = Button(self, text='Hello',

command=self.onPress)

widget.pack(side=LEFT)

def onPress(self):

print 'Hi.' # write to stdout

if __name__ == '__main__': Hello().mainloop()

% hello.py

Hi.

OOP: Reusing GUIs by subclassing, ‘is-a’

♦ GUI classes can be extended by inheritance

♦ Subclasses may extend, or replace methods

♦ In OOP terms: a ‘is-a’ relationship

file: hellosub.py

#!/usr/local/bin/python

from hello import Hello # get superclass

from Tkinter import * # get Tkinter widgets

class HelloExtender(Hello): # is-a hello.Hello

def make_widgets(self): # extend method

Hello.make_widgets(self)

mine = Button(self, text='Extend',

command=self.quit)

mine.pack(side=RIGHT)

def onPress(self):

print 'Greetings!' # replace method

if __name__ == '__main__': HelloExtender().mainloop()

% python hellosub.py

Greetings!

OOP: Reusing GUIs by attaching, ‘has-a’

♦ Frames can be attached to other Frames

♦ Tkinter records object tree internally

♦ In OOP terms: a ‘has-a’ relationship

file: hellouse.py

#!/usr/local/bin/python

from hello import Hello # get class to attach

from Tkinter import * # get Tkinter widgets

class HelloContainer(Frame): # has-a hello.Hello

def __init__(self, parent=None):

Frame.__init__(self, parent)

self.pack()

self.make_widgets()

def make_widgets(self):

mine = Button(self, text='Attach',

command=self.quit)

mine.pack(side=LEFT)

Hello(self) # attach a Hello to me

if __name__ == '__main__': HelloContainer().mainloop()

% hellouse.py

Hi.

Images

See “Extras\Code\Gui\Code” directory on class CD to run this example

As of Python 3.4, tkinter supports PNG, GIF, amd PPM/PPG; install Pillow for others

from Tkinter import * # get base widget set

from glob import glob # file name expansion

import hellouseCheck # attach the last example to "me"

import random # pick a picture at random

gifdir = '../../../Part3/Gui/gifs/' # where to look for gif files

def draw():

name, photo = random.choice(images)

lbl.config(text=name)

pix.config(image=photo)

root=Tk()

lbl = Label(root, text="none", bg='blue', fg='red')

pix = Button(root, text="Press me", command=draw, bg='white')

lbl.pack(fill=BOTH)

pix.pack(pady=10)

hellouseCheck.HelloContainer(root, relief=SUNKEN, bd=2).pack(fill=BOTH)

files = glob(gifdir + "*.gif")

images = map(lambda x: (x, PhotoImage(file=x)), files)

print files

root.mainloop()

Grid layouts

# 2d table of input fields

# see also frigcal’s uniform gridding: tables

from Tkinter import *

rows = []

for i in range(5):

cols = []

for j in range(4):

e = Entry(relief=RIDGE)

e.grid(row=i, column=j, sticky=NSEW)

e.insert(END, '%d.%d' % (i, j))

cols.append(e)

rows.append(cols)

def onPress():

for row in rows:

for col in row:

print col.get(),

Button(text='Fetch', command=onPress).grid()

mainloop()

Canvas, Text, dialogs, and Toplevel

(Some of the following may be in 2.X form: convert to run on 3.X)

See Extras\Code\Gui\Code to run this example

Larger examples: Programming Python, Editions 2+

See learning-python.com/gadgets for more sceenshots

See CD’s top-level Extras\PP4E-Examples folder for code

Also available at http://learning-python.com/books/about-pp4e.html

A clock drawn on a canvas and updated with a timer, embedded picture

A calculator: frames of buttons, popup history, command lines, key bindings

An artificially intelligent tic-tac-toe game: labels and mouse event bindings

A text editor object/program: menus, text, scrollbars, toolbar frame (old, new)

A photo viewer, with thumbnails, resizing

A demo launcher button bar: os.fork() on Linux, os.spawnv() on Windows

A generic tree data structure drawer: canvas, lines, event bindings

An image file slideshow: embeds text editor, picture, scale, timer, etc.

A table browser GUI: listboxes, forms, persistence, etc.

A drawing program: draw and move graphic objects

A POP/SMTP email client in Python/Tk, embeds text editor (old, new)

Larger Examples: frigcal, mergeall (2015)

See CD’s top-level Extras\frigcal-mergeall folder

Click images below for larger versions on the web

$Description: Description: Description: C:\Users\mark\Desktop\000-latest-composite.png$

$Description: Description: Description: C:\Users\mark\Desktop\main-quit-help.png$

Tkinter odds and ends

♦ Portability

● [tT]kinter programs run with native look-and-feel on X, MS-Windows, Macintosh

● Vast majority of code runs unchanged across different platforms

● But some aspects are platform-specific, especially window manager context (icons, modal dialogs)

♦ Other GUI widgets

● 25 widgets + dialogs, etc,: Text, Canvas, Listbox, Scrollbar, Image, Menu, Entry, Radiobutton, Checkbutton, Scale,…

♦ Other Tkinter tools

● File handlers, scheduled events, “grid” manager, drag-and-drop, tix and themes

● Pmw (Python Mega Widgets), PIL (imaging), etc.; see Vaults site

● Interactive GUI builders: PythonWorks?, ActiveState Komodo

● BoaConstructor, BlackAdder Gui buildes for wxPython, PyQt

♦ Implementation structure

● Tk + C extension module + Python wrapper classes module

● Uses extending (Tk lib) plus embedding (route events to handlers)

♦ Documentation

● “Programming Python 2^nd Edition”, Part II, 250 pages

● “Programming Python 3^rd Edition”, Part II, 300 pages

● “Programming Python 4^th Edition”, Part III 400 pages, + other parts: email client

● Other books: Manning book (somewhat dated), and others (see Amazon)

● Tcl/Tk books and manuals also provide basic widget docs

● Tutorial, reference: http://effbot.org/tkinterbook/

● Reference: http://infohost.nmt.edu/tcc/help/pubs/tkinter/web/index.html

● Wiki: https://wiki.python.org/moin/TkInter

♦ Other links

Extras\Code\Gui\wxPython\wxPython.doc (Tkinter/wxPython comparison)

Extras\Code\Gui\Code (additional Tkinter examples)

Extras\PP3E-Examples (book GUI examples, Python 2.X)

Extras\PP4E-Examples (book GUI examples, Python 3.X)

Lab Session 8

Click here to go to lab exercises

Click here to go to exercise solutions

Click here to go to solution source files

Click here to go to lecture example files