Why Do Tkinter Images Disappear When Created Within Class Methods?

Understanding Tkinter Image Visibility Issues

Tkinter, a popular GUI library for Python, occasionally encounters issues with displaying images when created within functions. This behavior stems from how Tkinter handles local variables like image references.

The Challenge

Consider the following code that successfully displays an image:

import tkinter

root = tkinter.Tk()
canvas = tkinter.Canvas(root)
canvas.grid(row = 0, column = 0)
photo = tkinter.PhotoImage(file = './test.gif')
canvas.create_image(0, 0, image=photo)
root.mainloop()

However, when creating the image within a class method, the image disappears.

import tkinter

class Test:
    def __init__(self, master):
        canvas = tkinter.Canvas(master)
        canvas.grid(row = 0, column = 0)
        photo = tkinter.PhotoImage(file = './test.gif')
        canvas.create_image(0, 0, image=photo)

root = tkinter.Tk()
test = Test(root)
root.mainloop()

The Solution

The issue arises because the local variable photo represents a reference to the image. In the class method, this reference is lost because photo goes out of scope after the method is executed.

To resolve this, save a persistent reference to the photo within the class instance:

import tkinter

class Test:
    def __init__(self, master):
        canvas = tkinter.Canvas(master)
        canvas.grid(row = 0, column = 0)
        self.photo = tkinter.PhotoImage(file = './test.gif')
        canvas.create_image(0, 0, image=self.photo)

root = tkinter.Tk()
test = Test(root)
root.mainloop()

By storing the reference in self.photo, it persists for the lifetime of the class instance, ensuring the image remains visible.

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