heapq.py imports doctest in the last 4 lines to perform unit tests:

    if __name__ == "__main__":
    
        import doctest # pragma: no cover
        print(doctest.testmod()) # pragma: no cover

This disrupts dependency tracking modules and software, like modulegraph and pyinstaller, as doctest brings in many dependencies (including ctypes as of 3.8).

This functionality could be factored out into a separate unit-testing file.