I tried to come up with an image demo for this section that was both fun and useful. I settled for the fun part. Example 9-39 displays a button that changes its image at random each time it is pressed.

from Tkinter import *                # get base widget set
from glob import glob                # filename expansion list
import demoCheck                     # attach checkbutton demo to me
import random                        # pick a picture at random
gifdir = '../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)
demoCheck.Demo(root, relief=SUNKEN, bd=2).pack(fill=BOTH)

files = glob(gifdir + "*.gif")                              # GIFs for now
images = map((lambda x: (x, PhotoImage(file=x))), files)    # load and hold
print files
root.mainloop( )

This code uses a handful of built-in tools from the Python library:

Just for fun, this script also attaches an instance of the demoCheck check button demo bar, which in turn attaches an instance of the Quitter button we wrote earlier. This is an artificial example, of course, but again it demonstrates the power of component class attachment at work.

Notice how this script builds and holds on to all images in its images list. The map here applies a PhotoImage constructor call to every .gif file in the photo directory, producing a list of (file,image) tuples that is saved in a global variable (a list comprehension [(x, PhotoImage(file=x)) for x in files] would do the same). Remember, this guarantees that image objects won’t be garbage collected as long as the program is running. Figure 9-39 shows this script in action on Windows.

Figure 9-39. buttonpics in action

Although it may not be obvious in this grayscale book, the name of the GIF file being displayed is shown in red text in the blue label at the top of this window. This program’s window grows and shrinks automatically when larger and smaller GIF files are displayed; Figure 9-40 shows it randomly picking a taller photo globbed from the image directory.

Figure 9-40. buttonpics showing a taller photo

And finally, Figure 9-41 captures this script’s GUI displaying one of the wider GIFs, selected completely at random from the photo file directory.^[*]

Figure 9-41. buttonpics gets political

While we’re playing, let’s recode this script as a class in case we ever want to attach or customize it later (it could happen). It’s mostly a matter of indenting and adding self before global variable names, as shown in Example 9-40.

from Tkinter import *                # get base widget set
from glob import glob                # filename expansion list
import demoCheck                     # attach check button example to me
import random                        # pick a picture at random
gifdir = '../gifs/'                  # default dir to load GIF files

class ButtonPicsDemo(Frame):
    def _ _init_ _(self, gifdir=gifdir, parent=None):
        Frame._ _init_ _(self, parent)
        self.pack( )
        self.lbl = Label(self,  text="none", bg='blue', fg='red')
        self.pix = Button(self, text="Press me", command=self.draw, bg='white')
        self.lbl.pack(fill=BOTH)
        self.pix.pack(pady=10)
        demoCheck.Demo(self, relief=SUNKEN, bd=2).pack(fill=BOTH)
        files = glob(gifdir + "*.gif")
        self.images = map(lambda x: (x, PhotoImage(file=x)), files)
        print files

    def draw(self):
        name, photo = random.choice(self.images)
        self.lbl.config(text=name)
        self.pix.config(image=photo)

if _ _name_ _ == '_ _main_ _': ButtonPicsDemo().mainloop( )

This version works the same way as the original, but it can now be attached to any other GUI where you would like to include such an unreasonably silly button.