Check for Match instance in Union[Match, str]

[mkurnikov]

It's not clear for me, how should I use Pattern and Match type aliases to pick apart Union[Match, str].

It looks like Match type alias supports __subclasscheck__, but mypy used with

from typing import Match, Union

def process_consumed_issubclass(consumed: Union[Match, str]) -> str:
    if issubclass(type(consumed), Match):
        return consumed.group('res')

    return consumed

returns

test_mypy_match.py: note: In function "process_consumed_issubclass":
test_mypy_match.py:7: error: Some element of union has no attribute "group"
test_mypy_match.py:9: error: Incompatible return value type (got "Union[Match[Any], str]", expected "str")

Match.impl_type have type(stdlib_re.match('', '')), but isinstance check still doesn't work

def process_consumed_isinstance(consumed: Union[Match, str]) -> str:
    if isinstance(consumed, Match.impl_type):
        return consumed.group('res')

    return consumed

test_mypy_match.py: note: In function "process_consumed_isinstance":
test_mypy_match.py:13: error: Match[AnyStr] has no attribute "impl_type"
test_mypy_match.py:14: error: Some element of union has no attribute "group"
test_mypy_match.py:16: error: Incompatible return value type (got "Union[Match[Any], str]", expected "str")

mypy 0.4.5, cpython 3.5.2.

[gvanrossum]

Can you use the reverse check, i.e. `if not isinstance(consumed, str)`?

[mkurnikov]

Reverse check works fine, thanks. The issue was meant to be a bug report, feel free to close it, if it's irrelevant.

[gvanrossum]

Hm, mypy doesn't understand issubclass(type(x), C) at all, and in general that should just be written using isinstance() (which works in mypy). But I understand that typing.py doesn't support this, even though it should. Can you file a bug about that in https://github.com/python/typing/issues ?

[mkurnikov]

It looks like it's fixed in python/typing already with python/typing#283:
https://github.com/python/typing/blame/master/src/typing.py#L312
It just hasn't been released yet.

[gvanrossum]

Thanks!