Python Tkinter Simple Qn

[Eric Brunel]

In article 
<ecd3ebca-8192-445a-a60c-c688b18f4287 at i4g2000prf.googlegroups.com>,
 ChrisChia <chrischia82 at gmail.com> wrote:

> Hi i have the following problem with Python Tkinter.
> I switch to switch the image background (which i used Tkinter.Label
> with image arg to display on the GUI).
> 
> How can I do that? the callback function which i have created doesn't
> seem to work...

It is usually way better to post the actual error than just saying 
"doesn't seem to work"Š Here your problem is quite clear, but in most 
circumstances, it would be quite difficult to figure out what's 
happening.

> some advice?
> 
> below is my code:
> 
> 
> import Tkinter as tk
> from PIL import Image, ImageTk
> 
> root = tk.Tk()
> 
> # having problem with switching the image
> def callback(event):
>     global root
>     root.panel1.pack_forget()
>     root.panel1.image = image2

The variable image2 is not known in this context, so no wonder the 
callback doesn't work. Let me guess: it says something like "NameError: 
name 'image2' is not defined"?

>     root.panel1.pack()
> 
> 
> def app():
> 
>     root.title('FIT 2022 Assignment 1')
> 
>     # pick an image file you have .bmp .jpg .gif. .png
>     # load the file and covert it to a Tkinter image object
>     imageFile = "c:\\test1.jpg"
>     image1 = ImageTk.PhotoImage(Image.open(imageFile))
>     imageFile2 = "c:\\test2.jpg"
>     image2 = ImageTk.PhotoImage(Image.open(imageFile2))

Here, you create image2 as a local variable in function app. So the 
variable name will not be known outside of app. If you want it to be 
global, you have to add a line:
global image2
at the beginning of your app function. Then it should work correctly.

By the way, I usually find it better to organize a GUI into classes 
rather than using functions. This way, you could store the images in 
object attributes and define your callback as a method, and not as a 
function.

>     # get the image size
>     w = image1.width()
>     h = image1.height()
> 
> 
>     # position coordinates of root 'upper left corner'
>     x = 0
>     y = 0
> 
> 
>     # make the root window the size of the image
>     root.geometry("%dx%d+%d+%d" % (w, h, x, y))
> 
> 
>     # root has no image argument, so use a label as a panel
>     panel1 = tk.Label(root, image=image1)
>     panel1.pack(side='top', fill='both', expand='yes')
>     panel1.image = image1
>     panel1.bind("<Button-1>", callback)
> 
> 
>     panel1.pack()
>     root.mainloop()
> 
> 
> app()

HTH
 - Eric -