Unreached/Unreachable(?) paths in tslib

[jbrockmendel]

in tslib._Timedelta.__richcmp__ there is a path that is not reached in tests that I think may not be reachable, seeking second opinions. If there are corner cases where this can be reached, they should be added to the tests.

        if isinstance(other, _Timedelta):
            if isinstance(other, _NaT):
                return _cmp_nat_dt(other, self, _reverse_ops[op])

[gfyoung]

This looks reachable, given that _NaT subclasses _Timedelta. If you can write a test that hits this branch of logic, go for it! It seems feasible.

[jbrockmendel]

Are you sure _NaT subclasses _Timedelta? If so, can you help me understand how?

cdef class _NaT(_Timestamp):

[gfyoung]

Oops, I misread it as _Timestamp 😄 . My bad, yeah, I think you're probably right then, as I don't think datetime.datetime and datetime.timedelta inherit from one another (trace back the class inheritances for both _Timedelta and _NaT).

Double check and then try removing the check to see what happens.