Can't define a typing.Union containing a typing.re.Pattern

[MartCongostTapias]

BPO	25390
Nosy	@gvanrossum, @zhangyangyu

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/gvanrossum'
closed_at = <Date 2015-10-19.21:57:04.177>
created_at = <Date 2015-10-13.09:27:47.517>
labels = ['type-bug', 'library']
title = "Can't define a typing.Union containing a typing.re.Pattern"
updated_at = <Date 2015-10-19.21:57:04.176>
user = 'https://bugs.python.org/MartCongostTapias'

bugs.python.org fields:

activity = <Date 2015-10-19.21:57:04.176>
actor = 'gvanrossum'
assignee = 'gvanrossum'
closed = True
closed_date = <Date 2015-10-19.21:57:04.177>
closer = 'gvanrossum'
components = ['Library (Lib)']
creation = <Date 2015-10-13.09:27:47.517>
creator = 'Mart\xc3\xad Congost Tapias'
dependencies = []
files = []
hgrepos = []
issue_num = 25390
keywords = []
message_count = 3.0
messages = ['252923', '252937', '253198']
nosy_count = 4.0
nosy_names = ['gvanrossum', 'python-dev', 'xiang.zhang', 'Mart\xc3\xad Congost Tapias']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue25390'
versions = ['Python 3.5']

[MartCongostTapias]

Defining a union of typing.re.Pattern and anything that isn't AnyStr raises a TypeError exception.

Example:

from typing import Union, re

def foo(pattern: Union[str, re.Pattern]) -> None:
    pass

Exception traceback:

Traceback (most recent call last):
  File "/tmp/testtyping.py", line 7, in <module>
    def foo(pattern: Union[str, re.Pattern]) -> None:
  File "/usr/local/lib/python3.5/typing.py", line 534, in __getitem__
    dict(self.__dict__), parameters, _root=True)
  File "/usr/local/lib/python3.5/typing.py", line 491, in __new__
    for t2 in all_params - {t1} if not isinstance(t2, TypeVar)):
  File "/usr/local/lib/python3.5/typing.py", line 491, in <genexpr>
    for t2 in all_params - {t1} if not isinstance(t2, TypeVar)):
TypeError: issubclass() arg 1 must be a class

[gvanrossum]

Confirmed. The failure is because Pattern is _TypeAlias, which is not a type. But it should be allowed. I'll think of something. (Does mypy accept this?)

[python-dev]

New changeset 955d3faf727a by Guido van Rossum in branch '3.5':
Issue bpo-25390: typing: Don't crash on Union[str, Pattern].
https://hg.python.org/cpython/rev/955d3faf727a

New changeset 04314479af0b by Guido van Rossum in branch 'default':
Issue bpo-25390: typing: Don't crash on Union[str, Pattern]. (Merge 3.5->3.6)
https://hg.python.org/cpython/rev/04314479af0b