maximum recursion depth when using typing options

[RoyShmueli]

BPO	27014
Nosy	@gvanrossum
Files	bug.py: a file that replicates the bug

^{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 2016-05-18.15:46:14.107>
created_at = <Date 2016-05-13.12:57:16.728>
labels = ['type-crash']
title = 'maximum recursion depth when using typing options'
updated_at = <Date 2016-05-18.15:46:14.105>
user = 'https://bugs.python.org/RoyShmueli'

bugs.python.org fields:

activity = <Date 2016-05-18.15:46:14.105>
actor = 'gvanrossum'
assignee = 'gvanrossum'
closed = True
closed_date = <Date 2016-05-18.15:46:14.107>
closer = 'gvanrossum'
components = []
creation = <Date 2016-05-13.12:57:16.728>
creator = 'Roy Shmueli'
dependencies = []
files = ['42840']
hgrepos = []
issue_num = 27014
keywords = []
message_count = 7.0
messages = ['265473', '265499', '265566', '265787', '265789', '265830', '265831']
nosy_count = 3.0
nosy_names = ['gvanrossum', 'python-dev', 'Roy Shmueli']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue27014'
versions = ['Python 3.5', 'Python 3.6']

[RoyShmueli]

While creating class of List and using a Optional as part of the typing system. I have got an error when I was importing one of my module. I was able to simplify the problem by creating a one module that replicate the crash.

[gvanrossum]

Ow, that's bad. :-(

Great job reducing this to a minimal repro!

I'm guessing it's got to do with registration. I'll try to figure out how to fix it; the fix should appear in Python 3.5.2.

[gvanrossum]

Simpler repro:

from collections import UserList
from typing import Sequence
class MyList(UserList, Sequence):
    pass
isinstance(None, Sequence)

No progress yet in understanding. :-(

[gvanrossum]

See also python/mypy#1546 -- possibly it's the same issue.

[gvanrossum]

Actually, see python/typing#222 instead.

[python-dev]

New changeset 79197e60e441 by Guido van Rossum in branch '3.5':
Fix bpo-27014 -- infinite recursion using typing.py.
https://hg.python.org/cpython/rev/79197e60e441

New changeset a6c04626205f by Guido van Rossum in branch 'default':
Fix bpo-27014 -- infinite recursion using typing.py. (Merge 3.5 -> 3.6.)
https://hg.python.org/cpython/rev/a6c04626205f

[gvanrossum]

Thanks to Kalle Tuure for the fix!