Type (typing) objects are hashable and comparable for equality but this is not documented

[gareth-rees]

BPO	27588
Nosy	@gvanrossum, @gareth-rees, @ilevkivskyi

^{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 = None
closed_at = <Date 2016-10-09.03:18:21.197>
created_at = <Date 2016-07-22.09:50:51.088>
labels = ['type-feature', 'docs']
title = 'Type (typing) objects are hashable and comparable for equality but this is not documented'
updated_at = <Date 2016-10-09.03:18:21.179>
user = 'https://github.com/gareth-rees'

bugs.python.org fields:

activity = <Date 2016-10-09.03:18:21.179>
actor = 'gvanrossum'
assignee = 'docs@python'
closed = True
closed_date = <Date 2016-10-09.03:18:21.197>
closer = 'gvanrossum'
components = ['Documentation']
creation = <Date 2016-07-22.09:50:51.088>
creator = 'gdr@garethrees.org'
dependencies = []
files = []
hgrepos = []
issue_num = 27588
keywords = []
message_count = 3.0
messages = ['270981', '270997', '278337']
nosy_count = 4.0
nosy_names = ['gvanrossum', 'docs@python', 'gdr@garethrees.org', 'levkivskyi']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue27588'
versions = ['Python 3.5', 'Python 3.6']

[gareth-rees]

The type objects constructed by the metaclasses in the typing module are hashable and comparable for equality:

    >>> from typing import *
    >>> {Mapping[str, int], Mapping[int, str]}
    {typing.Mapping[int, str], typing.Mapping[str, int]}
    >>> Union[str, int, float] == Union[float, int, str]
    True
    >>> List[int] == List[float]
    False

but this is not clearly documented in the documentation for the typing module (there are a handful of examples using equality, but it's not explicit that these are runnable).

It would be nice if there were explicit documentation for these properties of type objects.

[ilevkivskyi]

I am not sure that this feature will survive the resolution of python/typing#136

Types in typing are primarily intended for use with static type checkers and similar tools, their runtime properties are still under some discussions.

[gvanrossum]

Fixed by the changes for issue bpo-28388.