This issue depends and follows-up on #27891, consistently grouping and sorting imports in idlelib files.

PEP 8 (also) says 'all imports are put at the top of the file', though the 'consistency hobgloblin' rule allows for exceptions.  Possible reasons include making circular imports work, delaying side-effects, and significantly reducing initial import time of the containing module.   All are rare.

Idlelib currently has numerous exceptions, only a few of which have a documented reason.  The others might have a good reason, but may be holdovers from when 'import at top' was absent or not observed.  I propose to at least document the exceptions by putting comments at the top, in their sort location among other idlelib imports.  Examples: 

# from idlelib import module  # in EditorWindow
# from idlelib.other import SomeClass  # in EditorWindow

Doing this will make it possible to see at a glance all the idlelib imports in a module.

I will remove at least one redundant delayed import and move some when I am sure there is no reason not to.  I may ask original authors as to their reason for placing imports where they did.

Moving 'import X' from a function is easy and safe.  Moving an import from a class requires deleting 'self.' from all references, so is not safe without extra care.  At least for EditorWindow, I may leave this to when editing the class anyway.

Another good reason for delaying an import is when the import is only needed for testing.

In module_x
...
def callable_x(parent)  # htest #
    from tkinter import Toplevel
    box = Toplevel(parent)
    ...
if __name__ == '__main__':
    from unittest import main
    main('idlelib.idle_test.test_module_x', verbosity=2)

    from idlelib.idle_test.htest import run
    run(callable_x)

This should be part of 'Import Standards' in idlelib.README.