When running python -S, attempting to run "import genericpath" fails with an attribute error due to a circular dependency between posixpath and genericpath that's triggered when "import os" is called from within genericpath.py. 

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/fbcode/platform007/lib/python3.7/genericpath.py", line 6, in <module>
    import os
  File "/usr/local/fbcode/platform007/lib/python3.7/os.py", line 57, in <module>
    import posixpath as path
  File "/usr/local/fbcode/platform007/lib/python3.7/posixpath.py", line 130, in <module>
    splitext.__doc__ = genericpath._splitext.__doc__
AttributeError: module 'genericpath' has no attribute '_splitext'