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bpo-34498: Warn against using deprecated typing aliases with @singledispatch - #29508

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bpo-34498: Warn against using deprecated typing aliases with @singledispatch#29508
AlexWaygood wants to merge 2 commits into
python:mainfrom
AlexWaygood:functools-docs-typing-module

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@AlexWaygood

@AlexWaygood AlexWaygood commented Nov 9, 2021 •
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Attempting to register a singledispatch implementation on certain aliases
from the typing module will lead to an exception being raised. Since these
aliases are all deprecated, this PR proposes simply adding a note to the
documentation steering users towards PEP 585-style syntax.

https://bugs.python.org/issue34498

@AlexWaygood
bpo-34498: Warn against using deprecated typing aliases with ``@s…
111a1fa 
…ingledispatch``

Attempting to register a ``singledispatch`` implementation on certain aliases
from the ``typing`` module will lead to an exception being raised. Since these
aliases are all deprecated, this PR proposes simply adding a note to the
documentation steering users towards PEP 585-style syntax.
@bedevere-bot bedevere-bot added docs Documentation in the Doc dir awaiting review labels Nov 9, 2021
akulakov
akulakov reviewed Dec 4, 2021
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Comment thread Doc/library/functools.rst
akulakov
akulakov reviewed Dec 4, 2021
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Comment thread Doc/library/functools.rst Outdated
@akulakov

akulakov commented Dec 4, 2021

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Other than 2 minor comments, looks good to me.

@AlexWaygood

AlexWaygood commented Dec 4, 2021

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Other than 2 minor comments, looks good to me.

Thanks for taking a look!

@AlexWaygood
AlexWaygood requested a review from akulakov December 4, 2021 11:41
akulakov
akulakov approved these changes Dec 10, 2021
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Thanks for making the changes, LGTM

@AlexWaygood

AlexWaygood commented Dec 10, 2021

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Thanks for making the changes, LGTM

It actually seems that this would be a bad change to make -- while registering an implementation to list[int] will not raise an exception, actually attempting to use the function will raise an exception. A bug report was just today filed relating to this: https://bugs.python.org/issue46032 (I wasn't previously aware that it didn't work). So, I shall close this PR for now. Thanks very much for taking the time to review, all the same! 🙂

@akulakov

akulakov commented Dec 10, 2021

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Note that the part about using list instead of typing.List is still valid.

@AlexWaygood

AlexWaygood commented Dec 10, 2021

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Note that the part about using list instead of typing.List is still valid.

True, but how many people on Python <3.9 use typing.List if they don't need to parameterise the list? I know when I was using 3.8, I always used builtin generics unless I needed to parameterise something.

@akulakov

akulakov commented Dec 10, 2021

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Yes, I agree; just wanted to note it for reference for the future if someone refers to this PR.

@AlexWaygood
AlexWaygood deleted the functools-docs-typing-module branch December 11, 2021 00:12
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@akulakov akulakov akulakov approved these changes
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