add __getitem__ to class types (#25664)
Summary:
Add magic method for `class_type[index]`. Since the compiler has custom logic for indexing this was not included with the other magic methods.
Fix for https://github.com/pytorch/pytorch/issues/25637
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25664
Differential Revision: D17214996
Pulled By: eellison
fbshipit-source-id: bf77f70851f6c3487147da710cc996624492a0c8
