gh-140481: avoid misleading exception in tk.Tk.__getitem__

[TheLizzard]

Before

Code like:

import tkinter as tk
root = tk.Tk()
print("background" in root)

Would throw a TypeError: can only concatenate str (not "int") to str

Summary of changes

• Fixed the error message when calling "option" in <tk.Misc>
• Added __contain__ method to tk.Misc since it already has __getitem__ and __setitem__
• Added tests to prevent regression

Testing

• Ran ./python -m test test_tkinter -u=gui locally to make sure the old tests as well as the new ones pass

• Issue: Tkinter misleading error in Tk.__getitem__ #140481

[picnixz]

I'm not sure this is the correct way to fix this. We should instead check if option is a string in cget and if not raise a TypeError here.

cc @serhiy-storchaka

[TheLizzard]

That might be better but then for consistency sake, we would have to add a lot of type checks to functions like Misc.config since right now they raise TclError and not TypeError (root.config(background=frozenset()).

I don't know what the best course of action is.

[serhiy-storchaka]

See #140501.