Update typing module documentation based on PEP 585

[matusvalo]

BPO	40814
Nosy	@gvanrossum, @ilevkivskyi, @matusvalo, @DahlitzFlorian, @Fidget-Spinner
PRs	bpo-41805: Documentation for PEP 585 #22615

^{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 2020-10-31.17:37:43.363>
created_at = <Date 2020-05-29.12:28:33.397>
labels = ['type-bug', '3.9', '3.10', 'docs']
title = 'Update typing module documentation based on PEP 585'
updated_at = <Date 2020-10-31.17:37:43.363>
user = 'https://github.com/matusvalo'

bugs.python.org fields:

activity = <Date 2020-10-31.17:37:43.363>
actor = 'gvanrossum'
assignee = 'docs@python'
closed = True
closed_date = <Date 2020-10-31.17:37:43.363>
closer = 'gvanrossum'
components = ['Documentation']
creation = <Date 2020-05-29.12:28:33.397>
creator = 'Mat\xc3\xba\xc5\xa1 Valo'
dependencies = []
files = []
hgrepos = []
issue_num = 40814
keywords = ['patch']
message_count = 7.0
messages = ['370306', '372008', '374288', '378362', '378367', '378921', '380079']
nosy_count = 6.0
nosy_names = ['gvanrossum', 'docs@python', 'levkivskyi', 'Mat\xc3\xba\xc5\xa1 Valo', 'DahlitzFlorian', 'kj']
pr_nums = ['22615']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40814'
versions = ['Python 3.9', 'Python 3.10']

[matusvalo]

In documentation of typing module there is no mention of new possibilities based on PEP-585. Moreover, should be old constructs like List, Dict,... marked as deprecated?

[gvanrossum]

I don't think we should deprecate List etc. (PEP-585 specifically punts on the topic) but it's good to start mentioning list[t] etc. in the docs. Do you want to volunteer to write some docs?

[gvanrossum]

Alternatively, we at least need a section of documentation for things like list[int] and dict[str, float].

[Fidget-Spinner]

I've created a PR 22615 which partly addresses the documentation for GenericAlias in stdtypes.

I have a side question: should __args__, and __origin__ be documented somewhere as well? I noticed it has no documentation even though it's used to check generics. At the same time, I'm not fully sure that it's a standard Python thing rather than a CPython implementation detail.

[gvanrossum]

Yes, let’s document __args__ and __origin__.