从另一个类调用__init__中的类函数？

Question

First important note, I'm using tkinter. Each 'child' class has some unique widgets and functions, but every child class inherits the widgets and functions from the parent class (stuff like the background colour is defined here, because it's the same on every screen). When the user clicks certain buttons, the current class' screen is destroyed, and the next class is called. With that said, if I have a parent class like this:

class parent:
    def __init__(self):
        def back():
            if (someCondition == True):
                #some algorithm to go back, by deleting the current screen and popping the previous screen off a stack.
            else:
                change()

        #Algorithm to create main window
        self.back = Button(command=back)

And a child class like this

class child(parent):
    def __init__(self):
        parent.__init__(self)
        def change()
            #algorithm to change the contents of the screen, because in this unique case, I don't want to destroy the screen and call another one, I just want the contents of this screen to change.

        #Some algorithm to put unique widgets and such on this screen

How could I call the change() function from within the back() function? I tried 'child.change', but this returned an error message stating there was no attribute of 'child' called 'change'.

Answer 1

The solution is to make back a normal method. The parent can call methods of the child in the normal way.

class Parent(object):
    def back(self):
        print("in parent.back()")
        self.change()

class Child(Parent):
    def change(self):
        print("in child.change()")

# create instance of child
child = Child()

# call the back function:
child.back()

The above code yields the following output:

in parent.back()
in child.change()

If you prefer, you can make Parent.change() throw an error, to force the child to implement it:

class Parent(object):
    ...
    def change(self):
        raise Exception("Child must implement 'change'")

class MisfitChild(Parent):
    pass

With the above, the following will throw an error:

child = MisfitChild()
child.back()