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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.