Core Python Programming (2nd Edition)

Lines 3033
These lines represent our PFA magic. We use two levels of PFA. The first templatizes the Button class
and the root window top. What this does is that every time we call MyButton, it will call Button (Tkinter.
Button() creates a button.) with top as its first argument. We have "frozen" this into MyButton.
The second level of PFA is where we use our first one, MyButton, and templatize that. We create separate
button types for each of our sign categories. When users create a critical button CritButton (by calling
it, e.g., CritButton()), it will then call MyButton along with the appropriate button callback and
background and foreground colors, which means calling Button with top, callback, and colors. Do you
see how it unwinds and goes down the layers until at the very bottom, it has the call that you would
have originally had to make if this feature did not exist yet? We repeat with Warn-Button and ReguButton.
Lines 3542
With the setup completed, we look at our list of signs and create them. We put together a Python
evaluatable string consisting of the correct button name, pass in the button label as the text argument,
and pack() it. If it is a critical sign, then we CAPITALIZE the button text, otherwise we titlecase it. This
last bit is done in line 39, demonstrating another feature introduced in Python 2.5, the temporary
operator. Then we take each button creation string and execute it with eval(), creating the buttons one
at a time and resulting in the graphic seen previously. Finally, we start the GUI by entering the main
event loop.
This application uses several Python 2.5 features, so you will not be able to run this with an older
version.
19.3.6. Intermediate Tkinter Example
We conclude this section with a larger example, listdir.py. This application is a directory tree traversal
tool. It starts in the current directory and provides a file listing. Double-clicking on any other directory in
the list causes the tool to change to the new directory as well as replace the original file listing with the
files from the new directory. The source code is given as Example 19.6.
Example 19.6. File System Traversal GUI (listdir.py)
This slightly more advanced GUI expands on the use of widgets, adding listboxes, text
entry fields, and scrollbars to our repertoire. There are also a good number of callbacks
such as mouse clicks, key presses, and scrollbar action.
1 #!/usr/bin/env python
2
3 import os
4 from time import sleep
5 from Tkinter import *
6
7 class DirList(object):
8
9 def __init__(self, initdir=None):
10 self.top = Tk()
11 self.label = Label(self.top,
12 text='Directory Lister v1.1')