Patrick Labatut 64289a491d Annotate dunder functions
Summary: Annotate the (return type of the) following dunder functions across the codebase: `__init__()`, `__len__()`, `__getitem__()`

Reviewed By: nikhilaravi

Differential Revision: D29001801

fbshipit-source-id: 928d9e1c417ffe01ab8c0445311287786e997c7c
2021-06-24 15:19:16 -07:00
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2021-06-24 15:19:16 -07:00