unpack Tuple[int, AnyStr] to _, Optional[str]

[dfroger]

I have problems with mkstemp, which return type is Tuple[int, AnyStr]. I can't assign the second returned value to an Optional[str]:

from typing import Optional
from tempfile import mkstemp

def foo(path: Optional[str]):
    if path is None:
        f, path = mkstemp('f')

With mypy 0.600 and Python 3.6.2, I get the error:

foo.py:8: error: Value of type variable "AnyStr" of "mkstemp" cannot be "Optional[str]"

[ilevkivskyi]

We are sorry for this. This is yet another duplicate of #4872 (already high priority). The current workaround is to use a temporary variable:

from typing import Optional
from tempfile import mkstemp

def foo(path: Optional[str]):
    if path is None:
        f, _path = mkstemp('f')
        path = _path  # add link to this issue for future readers of your code

[dfroger]

@ilevkivskyi great thanks for pointing to the duplicated (I would not have find it by myself) and for the workaround!