如何在不同的 class 中调用包含 function 的 function？

Question

I am using Tkinter in Python 3, and have two windows, each represented by a class. I need to click a button in WindowB (my second class) that runs a method from WindowA (my first class). This should be fine, however the method I am calling calls another method from WindowA (my first class). This results in the error: AttributeError: 'WindowB' object has no attribute 'functionB'. How would I fix this so I can run functionA in WindowB (2nd class) with no errors? Code:

from tkinter import *
from functools import partial

class WindowA(Frame):
    def __init__(self, master= None): # initialise Menu
        Frame.__init__(self, master) # initialise Frame
        self.master = master
        self.createWindow() # adds buttons

    def createWindow(self):
        self.pack(fill = BOTH, expand = 1)
        # lambda prevents self.changeWindow from executing before button pressed
        button1 = Button(self, text = 'Change to Window B', command = lambda: self.changeWindow(WindowB))
        button1.pack(fill = X, padx = 10, pady = 10)

        button2 = Button(self, text = 'Run Function A', command = lambda: self.functionA())
        button2.pack(fill = X, padx = 10, pady = 10)


    def changeWindow(self, object):
        root.withdraw()
        currentFrame = object(root)

    def functionA(self):
        print("I am function A.")
        self.functionB()

    def functionB(self):
        print("I am function B, called from function A.")

class WindowB(Toplevel):
    def __init__(self, master = None):
        Toplevel.__init__(self, master)
        self.master = master
        self.Window()

    def Window(self):
        button3 = Button(self, text = 'Run Function A', command = lambda:WindowA.functionA(self))
        button3.grid(row = 1, column = 0, padx = 10)

root = Tk()
app = WindowA(root)
root.mainloop()

Answer 1

The most common solution is to pass the instance of WindowA when creating WindowB , so that the latter can access methods in the former.

First, make sure that WindowB can accept the name of the other window:

class WindowB(Toplevel):
    def __init__(self, master = None, windowA=None):
        Toplevel.__init__(self, master)
        self.master = master
        self.windowA=windowA
        self.Window()

Next, pass self as the windowA parameter when creating the instance of WindowB . I renamed object to self since you're passing a class rather than an instance of the class:

class WindowA(Frame):
    ...
    def changeWindow(self, cls):
        root.withdraw()
        currentFrame = cls(root, windowA=self)

You can then use self.windowA to call any method in that object:

class WindowB(Toplevel):
    ...
    def Window(self):
        ...
        button3 = Button(self, text = 'Run Function A', command = lambda:self.windowA.functionA())
        ...

Answer 2

As an alternative answer, you could use the classmethod decorator:

    def functionA(self):
        print("I am function A.")
        WindowA.functionB()

    @classmethod
    def functionB(cls):
        print("I am function B, called from function A.")

Note I am calling WindowA.functionB()

Answer 3

You're almost there, you only need to change just one thing in tge Window() method of class WindowB . You need to change it to be like so:

button3 = Button(self, text = 'Run Function A', command = lambda:WindowA().functionA())
# instead of 
# button3 = Button(self, text = 'Run Function A', command = lambda:WindowA.functionA(self))

Answer 4

you have to create instance from WindowA class to use WindowA function

class WindowB(Toplevel):
    def __init__(self, master=None):
        Toplevel.__init__(self, master)
        self.master = master
        self.Window()
        self.WindowA = WindowA()  # added here

    def Window(self):
        button3 = Button(self, text='Run Function A', command=lambda: self.WindowA.functionA())
        button3.grid(row=1, column=0, padx=10)