backend.py: _getattr__ must raise AttributeError (#21763)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21763
Custom __getattr__ functions can only raise AttributeError. This code throwed NotImplementedError which caused upstream troubles when hasattr() was called.
Differential Revision: D15815176
fbshipit-source-id: 0982e2382de4578d3fc05c5d2a63f624d6b4765e
