Remove ParamSpec from __parameters__ of most typing generics

[Fidget-Spinner]

BPO	44098
Nosy	@gvanrossum, @serhiy-storchaka, @ilevkivskyi, @miss-islington, @Fidget-Spinner
PRs	bpo-44098: Drop ParamSpec from most __parameters__ in typing generics #26013 [3.10] bpo-44098: Drop ParamSpec from most __parameters__ in typing generics (GH-26013) #26091

^{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/Fidget-Spinner'
closed_at = <Date 2021-05-14.14:17:17.921>
created_at = <Date 2021-05-10.09:41:35.969>
labels = ['library', '3.10', '3.11']
title = 'Remove ParamSpec from __parameters__ of most typing generics'
updated_at = <Date 2021-07-31.13:36:10.523>
user = 'https://github.com/Fidget-Spinner'

bugs.python.org fields:

activity = <Date 2021-07-31.13:36:10.523>
actor = 'serhiy.storchaka'
assignee = 'kj'
closed = True
closed_date = <Date 2021-05-14.14:17:17.921>
closer = 'kj'
components = ['Library (Lib)']
creation = <Date 2021-05-10.09:41:35.969>
creator = 'kj'
dependencies = []
files = []
hgrepos = []
issue_num = 44098
keywords = ['patch']
message_count = 8.0
messages = ['393373', '393589', '393662', '398283', '398300', '398346', '398393', '398641']
nosy_count = 5.0
nosy_names = ['gvanrossum', 'serhiy.storchaka', 'levkivskyi', 'miss-islington', 'kj']
pr_nums = ['26013', '26091']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue44098'
versions = ['Python 3.10', 'Python 3.11']

[Fidget-Spinner]

typing.List includes ParamSpec in __parameters__ but the builtin list doesn't. The behavior of the latter is correct, as PEP-612 states that: "As before, parameters_expressions by themselves are not acceptable in places where a type is expected".

https://www.python.org/dev/peps/pep-0612/#valid-use-locations

This patch just makes the typing version same as the builtin version by excluding ParamSpec from __parameters__ (except for Concatenate, Callable, and Generic).

[gvanrossum]

New changeset c55ff1b by Miss Islington (bot) in branch '3.10':
bpo-44098: Drop ParamSpec from most __parameters__ in typing generics (GH-26013) (bpo-26091)
c55ff1b

[Fidget-Spinner]

All patches have landed. Thanks Guido!

[serhiy-storchaka]

I think that List[P] should be illegal at first place.

[gvanrossum]

Yeah, but we shouldn't go out of our way to reject it. Especially since in 3.11 we'll likely have something equivalent to PEP-563 or PEP-649 (the SC is thinking deep about this right now) and either of those means that usually it won't be evaluated at all anyway (you'd have to call get_type_hints() with PEP-563, or use __annotations__ with the other).

[serhiy-storchaka]

I am writing a patch which generalizes and significantly simplifies the code for type variables and parameter specifications substitution, and opens a way for more runtime validation. But it is incompatible with these changes.

[Fidget-Spinner]

@serhiy, could you please briefly describe what you are planning? I'm guessing you're generalizing for _TypeVarLike?

My main concern is that we should have as few differences between builtin and typing types as possible. typing.List is deprecated and set to remove in Python 3.13/14, so I'm hoping the transition will be fairly painless.

Originally, the builtin types supported ParamSpec, but I removed that in #69635 for various reasons listed in that PR.

[serhiy-storchaka]

See bpo-44796.