Use latest stable flake8-bugbear in CI and fix B011 flake8 error. (#21944)
Summary:
- PyCQA/flake8-bugbear#53 has been fixed (but not yet closed on their side) and a new version of flake8-bugbear has been released on Mar 28, 2019. Switch CI to use the latest stable version.
- Fix the new B011 errors that flake8-bugbear catches in the current codebase.
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B011: Do not call assert False since python -O removes these calls. Instead callers should raise AssertionError().
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21944
Differential Revision: D15974842
Pulled By: soumith
fbshipit-source-id: de5c2c07015f7f1c50cb3904c651914b8c83bf5c
