Refactor typing.TypedDict

[serhiy-storchaka]

BPO	40187
Nosy	@gvanrossum, @serhiy-storchaka, @ilevkivskyi
PRs	bpo-40187: Refactor typing.TypedDict. #19372

^{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 2020-04-08.08:05:53.116>
created_at = <Date 2020-04-04.21:20:39.697>
labels = ['type-feature', 'library', '3.9']
title = 'Refactor typing.TypedDict'
updated_at = <Date 2020-04-08.08:05:53.116>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2020-04-08.08:05:53.116>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2020-04-08.08:05:53.116>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2020-04-04.21:20:39.697>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 40187
keywords = ['patch']
message_count = 3.0
messages = ['365786', '365787', '365973']
nosy_count = 3.0
nosy_names = ['gvanrossum', 'serhiy.storchaka', 'levkivskyi']
pr_nums = ['19372']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue40187'
versions = ['Python 3.9']

[serhiy-storchaka]

typing.TypedDict is used in two ways.

1. It is a callable which produces a new pseudo-subtype of dict.
2. It can also be used as a base in the class statement for creating a new pseudo-subtype of dict.

In both cases it is not a real class. You cannot create an instance of TypedDict or its "subclass". isinstance() and issubclass() do not work with it. Instantiating it "subclass" always returns a dict. But it is implemented as a class, and help() shows methods and data descriptors for it, which are useless.

The proposed PR implements TypedDict as a function. It adds the __mro_entries__ method that allows to use it as a base in the class statement.

[serhiy-storchaka]

See also bpo-40185.

[serhiy-storchaka]

New changeset f228bf2 by Serhiy Storchaka in branch 'master':
bpo-40187: Refactor typing.TypedDict. (GH-19372)
f228bf2