bpo-42317: Improve docs of typing.get_args concerning Union by Dominik1123 · Pull Request #23254 · python/cpython · GitHub

https://bugs.python.org/issue42317

Automerge-Triggered-By: GH:gvanrossum

Suggested change

      
               If ``X`` is a :class:`Union`, the order of ``(Y, Z, ...)`` may be different
          
               If ``X`` is a :class:`Union` contained in another generic type, the order of ``(Y, Z, ...)`` may be different

This reverts commit 5a5ff4d.

I don't really like the current proposed change because it's too broad, it may cause users to worry that all nested types are affected, when in reality it's only Union.

Instead of:

If X is a generic type, the returned objects (Y, Z, ...) might not be identical to the ones used in the form X[Y, Z, ...] due to type caching.

Guido's change seems a lot more apt:

If X is a :class:Union contained in another generic type, the order of (Y, Z, ...) may be different

A quick search through the typing code tells me that only the __hash__ and __eq__ methods of Union are order independent, no other typing type will suffer from this behavior when nested in another Generic.

I don't really like the current proposed change because it's too broad, it may cause users to worry that all nested types are affected, when in reality it's only Union.

It's as broad as the promise of type caching goes, so I don't think it's too broad. But I agree that it's broader than necessary since indeed, at the moment, it requires a Union to be involved. Initially I thought it would also affect Literal, but apparently it doesn't:

>>> Literal[1, 2] == Literal[2, 1]
False

(Though I don't see why the two would be unequal; but that's a different concern)

Instead of:

If X is a generic type, the returned objects (Y, Z, ...) might not be identical to the ones used in the form X[Y, Z, ...] due to type caching.

Guido's change seems a lot more apt:

If X is a :class:Union contained in another generic type, the order of (Y, Z, ...) may be different

So I just revert back to Guido's version?

(Though I don't see why the two would be unequal; but that's a different concern)

Wow good catch, that looks like it may be a bug.

So I just revert back to Guido's version?

Maybe a combination of both yours and Guido's wording:

If `X` is a :class:`Union` contained in another generic type, the order of `(Y, Z, ...)` may be different due to type caching.

Btw, thank you for the PR!

…ric types

Thanks, LG!

Thanks @Dominik1123 for the PR 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖

…-23254) (cherry picked from commit c3b9592) Co-authored-by: Dominik1123 <15989985+Dominik1123@users.noreply.github.com>

GH-23307 is a backport of this pull request to the 3.9 branch.

(cherry picked from commit c3b9592) Co-authored-by: Dominik1123 <15989985+Dominik1123@users.noreply.github.com>

…-23254)

bpo-42317: Improve docs of typing.get_args concerning Union

5a5ff4d

Dominik1123 requested review from gvanrossum and ilevkivskyi as code owners November 12, 2020 20:38

the-knights-who-say-ni added the CLA signed label Nov 12, 2020

bedevere-bot added docs Documentation in the Doc dir awaiting review labels Nov 12, 2020

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Dominik1123 added 2 commits November 13, 2020 00:09

Revert "bpo-42317: Improve docs of typing.get_args concerning Union"

adc974d

This reverts commit 5a5ff4d.

bpo-42317: Improve docs of typing.get_args concerning generic types

633e736

Dominik1123 requested a review from gvanrossum November 13, 2020 08:18

bpo-42317: Improve docs of typing.get_args concerning Unions and gene…

e910d7f

…ric types

Fidget-Spinner approved these changes Nov 13, 2020

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bedevere-bot added awaiting core review and removed awaiting review labels Nov 13, 2020

gvanrossum added skip news needs backport to 3.9 labels Nov 16, 2020

gvanrossum approved these changes Nov 16, 2020

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bedevere-bot added awaiting merge and removed awaiting core review labels Nov 16, 2020

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miss-islington merged commit c3b9592 into python:master Nov 16, 2020

bedevere-bot removed the awaiting merge label Nov 16, 2020

bedevere-bot removed the needs backport to 3.9 label Nov 16, 2020

miss-islington added a commit that referenced this pull request Nov 16, 2020

bpo-42317 : Improve docs of typing.get_args concerning Union (GH-23254 )

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(cherry picked from commit c3b9592) Co-authored-by: Dominik1123 <15989985+Dominik1123@users.noreply.github.com>

Dominik1123 mentioned this pull request Nov 16, 2020

bpo-42345: Fix three issues with typing.Literal parameters #23294

Merged

adorilson pushed a commit to adorilson/cpython that referenced this pull request Mar 13, 2021

bpo-42317: Improve docs of typing.get_args concerning Union (pythonGH…

6e0be5b

…-23254)

                  For a typing object of the form ``X[Y, Z, ...]`` these functions return
                  ``X`` and ``(Y, Z, ...)``. If ``X`` is a generic alias for a builtin or
                  :mod:`collections` class, it gets normalized to the original class.
+                 If ``X`` is a :class:`Union`, the order of ``(Y, Z, ...)`` may be different

bpo-42317: Improve docs of typing.get_args concerning Union by Dominik1123 · Pull Request #23254 · python/cpython · GitHub

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bpo-42317: Improve docs of typing.get_args concerning Union - #23254

bpo-42317: Improve docs of typing.get_args concerning Union#23254
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	If ``X`` is a :class:`Union`, the order of ``(Y, Z, ...)`` may be different
	If ``X`` is a :class:`Union` contained in another generic type, the order of ``(Y, Z, ...)`` may be different

bpo-42317: Improve docs of typing.get_args concerning Union by Dominik1123 · Pull Request #23254 · python/cpython · GitHub

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bpo-42317: Improve docs of typing.get_args concerning Union - #23254

bpo-42317: Improve docs of typing.get_args concerning Union#23254miss-islington merged 4 commits intopython:masterpython/cpython:masterfrom Dominik1123:resolve-42317Dominik1123/cpython:resolve-42317Copy head branch name to clipboard

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bpo-42317: Improve docs of typing.get_args concerning Union#23254
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