Even after reading through #15061, I still wonder why _compare_digest is in _operator at all.  It makes even less sense to me to put a Python implementation in operator; shouldn't the Python implementation be in the module that actually uses it?

Branching from the recent discussion[1] about where to place a PBKDF2 wrapper, it would make the most sense to me to move hmac into hashlib as suggested and move _compare_digest into hashlib's C somewhere.

For the record, the reason I didn't try to implement a _compare_digest in operator.py in the first place was because #15061 made it pretty clear that operator.c was just a convenient place to stick the function, not that it was supposed to actually be part of the operator module.