confused about __init__ method inside of def __ini

问题:

In the following code:

import tkinter as tk

    class CardShuffling(tk.Tk):
        background_colour = '#D3D3D3'
        deck_size = 52

        def __init__(self):
            tk.Tk.__init__(self) # What does this do?

I am confused about the purpose of the last line.. an instance of CardShuffling inherits from tk.Tk, doesn't the last line just repeat what is already taken care of by CardShuffling(tk.Tk) ??

回答1:

CardShuffling(tk.Tk) only makes the class CardShuffling a child of tk.Tk. your new class inherits all the methods of this class.

but if you create a new object you still have to call the constructor of that base class (with the new object as argument). imagine there is a line self.a = 0 in the constructor of the parent class. your child class has to run this line when you initialize a new instance; CardShuffling(tk.Tk) can not do that for you; you need to run __init__ of the parent class.

the usual way to do that in python 3 is

def __init__(self):
    super().__init__()

which is the same in this case as

def __init__(self):
    tk.Tk.__init__(self)

maybe this article on inheritance helps and there is even a book chapter freely available.