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9796b9ed69
As pointed out by @gvanrossum in https://github.com/python/typing/issues/1096 Improves type inference in cases when we know that mode is OpenBinaryMode, but don't know anything more specific: ``` def my_open(name: str, write: bool): mode: Literal['rb', 'wb'] = 'wb' if write else 'rb' with open(name, mode) as f: reveal_type(f) # previously typing.IO[Any], now typing.BinaryIO ``` You may be tempted into thinking this is some limitation of type checkers. mypy does in fact have logic for detecting if we match multiple overloads and union-ing up the return types of matched overloads. The problem is the last overload interferes with this logic. That is, if you remove the fallback overload (prior to this PR), you'd get "Union[io.BufferedReader, io.BufferedWriter]" in the above example. Co-authored-by: hauntsaninja <>