Python: Import errors. Accessing method from other class

Question

I've got following problem: In my main tk window I have a button which opens a new Toplevel window. Once a button on the Toplevel window is clicked, a new element to a listbox should be added.

I keep getting this error message:

Traceback (most recent call last):
  File "MainWindow.py", line 4, in <module>
    from TopWindow import TopWindow
  File "TopWindow.py", line 4, in <module>
    import MainWindow
  File "MainWindow.py", line 4, in <module>
    from TopWindow import TopWindow
ImportError: cannot import name TopWindow

I believe the problem is that both classes import each other. However I am uncertain how to fix this. Any ideas?

Mainwindow.py:

from TopWindow import TopWindow

class MainWindow:
    def __init__(self, mainWindow):
        self.value = ''
        self.gui(mainWindow)
    def gui(self, mainWindow):
        top = TopWindow()
        button = tk.Button(optionFrame, text="Open TopWindow", command=top.import)
        ...

    def addtolistbox(self):
        ....


mainWindow = tk.Tk()
run = MainWindow(mainWindow)
mainWindow.mainloop()

TopWindow.py

import MainWindow
class TopWindow:
    def import(self):
        ....
        MainWindow.MainWindow().addtolistbox()

def import(self): i think it's your problem. it should be __init__() — Kobi K
– Kobi K, Commented Dec 17, 2013 at 14:22

Martijn Pieters · Accepted Answer · 2013-12-17 14:59:47Z

1

You created a circular import; when importing MainWindow from TopWindow, the TopWindow class is not yet defined, so the TopWindow module as seen by MainWindow doesn't have that attribute.

Postpone importing in the TopWindow class:

class TopWindow:
    def import(self):
        ....
        import MainWindow
        MainWindow.MainWindow().addtolistbox()

Next, you are creating a new copy of the MainWindow object each time; you probably want to access the singleton object created in MainWindow.run instead:

class TopWindow:
    def import(self):
        ....
        import MainWindow
        MainWindow.run.addtolistbox()

edited Dec 17, 2013 at 14:59

answered Dec 17, 2013 at 14:22

Martijn Pieters

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3 Comments

user3111516 Over a year ago

Thank you! That indeed fixes the import error. However, now I have a different problem. By calling MainWindow.MainWindow().addtolistbox(), I create a new Mainwindow instead of just updating the list on the existing window. I don't want a new MainWindow created, but a function called within the MainWindow to update the existing one. How would I do that?

user3111516 Over a year ago

In addition, the new MainWindow isn't in the mainloop anymore. I'm getting a TypeError: __init__() takes exactly 2 arguments (1 given)

Martijn Pieters Over a year ago

@user3111516: Perhaps you wanted to use MainWindow.run.addtolistbox() instead? You already created your main window object in that module.

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