fix tkinter master attributes

[Akuli]

All tkinter widgets have a master attribute. Tk is the only widget whose master attribute can be None (and Tk's master is always None). This is because of the way master widgets work in Tcl/Tk: a widget whose name in Tcl is .foo.bar has a master named .foo, and the master of .foo is the root widget named ., corresponding to an instance of tkinter.Tk.

You can also try running this to see the master attributes:

import tkinter.ttk

print(tkinter.Tk().master)
print(tkinter.Toplevel().master)
print(tkinter.Button().master)
print(tkinter.Canvas().master)
print(tkinter.Checkbutton().master)
print(tkinter.Entry().master)
print(tkinter.Frame().master)
print(tkinter.Label().master)
print(tkinter.Listbox().master)
print(tkinter.Menu().master)
print(tkinter.Menubutton().master)
print(tkinter.Message().master)
print(tkinter.Radiobutton().master)
print(tkinter.Scale().master)
print(tkinter.Scrollbar().master)
print(tkinter.Text().master)
print(tkinter.OptionMenu(None, tkinter.StringVar(), 'foo').master)
print(tkinter.Spinbox().master)
print(tkinter.LabelFrame().master)
print(tkinter.PanedWindow().master)
print(tkinter.ttk.Button().master)
print(tkinter.ttk.Checkbutton().master)
print(tkinter.ttk.Entry().master)
print(tkinter.ttk.Combobox().master)
print(tkinter.ttk.Frame().master)
print(tkinter.ttk.Label().master)
print(tkinter.ttk.Labelframe().master)
print(tkinter.ttk.Menubutton().master)
print(tkinter.ttk.Notebook().master)
print(tkinter.ttk.Panedwindow().master)
print(tkinter.ttk.Progressbar().master)
print(tkinter.ttk.Radiobutton().master)
print(tkinter.ttk.Scale().master)
print(tkinter.ttk.Scrollbar().master)
print(tkinter.ttk.Separator().master)
print(tkinter.ttk.Sizegrip().master)
print(tkinter.ttk.Treeview().master)
print(tkinter.ttk.LabeledScale().master)
print(tkinter.ttk.OptionMenu(None, tkinter.StringVar(), 'foo').master)

To verify that the stubs are correct, replace all prints with reveal_type and then mypying.

If something can be any widget, then the correct type for it is Misc, and that's why there's now a master attribute in Misc as well. So, if some_misc_instance.master is None is equivalent to (but more readable than) if isinstance(some_misc_instance, tkinter.Tk).

[Akuli]

@srittau Can you also review #4459 ?

[srittau]

When I find time.