in usort/config.py [0:0]
def known_factory() -> Dict[str, Category]:
known = {}
for name in STDLIB_TOP_LEVEL_NAMES:
known[name] = CAT_STANDARD_LIBRARY
# This is also in the stdlib list, so this override comes last...
known["__future__"] = CAT_FUTURE
known["__main__"] = CAT_FIRST_PARTY
return known