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 <>
* Replace all uses of StrPath, BytesPath, and AnyPath in Python 2 stubs.
* Add StrOrBytesPath as preferred alias for AnyPath.
* Replace all remaining AnyPath instances with StrOrBytesPath.
* Mark AnyPath as obsolete.
Part of #5470
Eliminated the use of "bare" TypeVars (i.e. a TypeVar that appears only once) within generic methods. While not considered an error in PEP 484, these are a common source of bugs in code, and some type checkers (including pytype and pyright) flag them as errors.
Co-authored-by: Eric Traut <erictr@microsoft.com>
