Add Attribute.alias by asford · Pull Request #950 · python-attrs/attrs

asford · 2022-04-09T20:23:27Z

Summary

PEP681 introduces an optional alias parameter to field descriptors, which specifies an alternative __init__ name for the member. This is not implemented in dataclasses, but is implemented in pydantic.

Add an explicit & overridable per-attribute alias in attrs, mirroring the behavior described in the PEP and dataclass_transform specification. This allows users to directly address the single largest incompatibility noted in the specification, attrs private attributes handling, which strips leading underscores from member names, discussed in #795.

This feature unblocks implementation of a shim layer to support attrs/dataclass interop, discussed in:

closes: #945
closes: #572

Goals:

This is silent no-op for "normal" users of attrs not using alias. Libraries building on attrs may use alias to detect both existing private-name init aliases and user-supplied aliases.
Add an alias : Optional[str] parameter to attr.ib et al and property to Attribute.
Lift current private-attribute-naming logic (name.lstrip("_")) into _ClassBuilder so that alias is always populated with the field's __init__ parameter name, regardless of whether an explicit alias is provided, during __init__ rendering and attr.fields introspection.
Leave Attribute.alias as None if not explicitly specified, so that field_transformer implementations can (a) create attributes without needing to be aware of alias and optionally provide alias overrides before attrs.
Update attr.evolve to use Attribute.alias rather than re-implemented name-mangling.
Update the attribute and private-attribute-handling documentation to note the new alias parameter.
Expand dataclass_transform documentation to describe how alias can be used to inform type checkers of private-name renaming behavior.
Politely file a bug against attrs noting the inconsistency between documentation and behavior. Dunder-methods are still affected by attr.ibs that will be __name-mangled should be attrs-init-mangled to <name> not ClassName_<name> #619, but evolve failures in pathological cases are resolved.
File a tracking issue against against cattrs to access Attribute.alias during codegen iff available in attrs: Use Attribute.alias for init argument names if attrs>= 2022.2 cattrs#322

Non-goals:

Modification of the existing private-attribute-naming logic, though could be tackled pre-release in a follow-up PR.

Pull Request Check List

docs/extending.rst

hynek

This looks all very good and thorough, just a bunch of questions and nits.

it also needs a newsfragment. make it sounds excited. :)

sorry for taking so long…whenever Attribute changes the diffs make me wann hide under the bed.

src/attr/_make.py

docs/extending.rst

src/attr/_funcs.py

src/attr/_make.py

docs/init.rst

hynek · 2022-05-25T07:30:05Z

Anything you need from my end? 😇

for more information, see https://pre-commit.ci

asford

My turn to apologize for the slow turnaround.

I've applied the review comments, and believe this is ready for a final pass.

docs/init.rst

src/attr/_make.py

hynek · 2022-11-16T15:03:17Z

w00t! Thanks for coming back! I'll try to be faster this time! :)

asford · 2022-11-16T15:30:32Z

Really appreciate your work on attrs.
Thanks for being stoked on the contribution!

hynek

Nailed it a tiny nit aside!

Thank you so much for coming back, I know how difficult it is to pick up something like this after a long time.

src/attr/_make.py

Tinche · 2022-11-30T14:41:49Z

Cool. Cattrs will be no problem, I can just bump the dependency to the latest version of attrs and implement it.

Mypy will be a bigger issue I think.

hynek · 2022-11-30T14:42:41Z

given alias is a dataclass transform feature, shouldn't it work OOB?

Tinche · 2022-11-30T14:43:49Z

Unsure, Mypy has a custom attrs plugin so I don't know if the dataclass_transform code path is in charge of this.

hynek · 2022-11-30T14:59:45Z

aw looks like you're right. pyright works: #1063

mypy doesn't:

Adding

AliasExample(without_alias=42, _with_alias=23)

gives me: tests/typing_example.py:134: error: Unexpected keyword argument "_with_alias" for "AliasExample"; did you mean "with_alias" or "without_alias"?

@Tinche 🐶🥺?

Tinche · 2022-11-30T15:00:46Z

Yeah, yeah. But we'd need to release attrs first.

hynek · 2022-11-30T15:14:54Z

yeah, it's super overdue too.

i'll try to get #1003 in ASAP (it's just an alias, so it should be just busywork) and push it out RSN.

Since the attrs version release, pub tests have begun failing with the error "TypeError: keywords must be strings". Attrs have added an "alias" parameter to each attribute[1], which is used in the attrs's "evolve" method to construct a new instance. This causes issues with the attribute "from", which has some special logic implemented in order to be usable at all[2]. The attribute "from" is generated from "from_", copying all its parameters. Since "alias" is a new parameter, it isn't copied and thus its value is set no "None". attrs's "evolve" method uses **kwargs to create a new instance, and it sets one of the keys in **kwargs to "None" (from alias). Keys in **kwargs must be strings, which causes the TypeError. It can be fixed by also setting "alias" in the newly created "from" attribute. In case of "from_", it has the same value as "name" parameter ("from_"), which is why we don't want to copy it from the old attribute, but explicitly set it to "from" (otherwise it would be "from_"). The change should be backwards compatible with older versions of attrs. [1] python-attrs/attrs#950 [2] release-engineering#108

Since new attrs version release, pub tests have begun failing with the error "TypeError: keywords must be strings". Attrs have added an "alias" parameter to each attribute[1], which is used in the attrs's "evolve" method to construct a new instance. This causes issues with the attribute "from", which has some special logic implemented in order to be usable at all[2]. The attribute "from" is generated from "from_", copying all its parameters. Since "alias" is a new parameter, it isn't copied and thus its value is set no "None". attrs's "evolve" method uses **kwargs to create a new instance, and it sets one of the keys in **kwargs to "None" (from alias). Keys in **kwargs must be strings, which causes the TypeError. It can be fixed by also setting "alias" in the newly created "from" attribute. In case of "from_", it has the same value as "name" parameter ("from_"), which is why we don't want to copy it from the old attribute, but explicitly set it to "from" (otherwise it would be "from_"). The change should be backwards compatible with older versions of attrs. [1] python-attrs/attrs#950 [2] release-engineering#108

asford mentioned this pull request Apr 9, 2022

Add PEP681 explicit & overridable per-attribute __init__ alias. #945

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asford commented Apr 9, 2022

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asford force-pushed the attrib_alias branch from 1664c1b to be899e8 Compare April 9, 2022 20:58

hynek mentioned this pull request Apr 29, 2022

Add attribute alias to attrs.field #953

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hynek requested changes May 2, 2022

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hynek mentioned this pull request Jun 24, 2022

Add support for Python 3.11 #969

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hynek added this to the 22.2.0 milestone Aug 11, 2022

asford and others added 11 commits November 13, 2022 07:57

Spike alias implementation.

210d93c

Move default alias init to after field_transformer.

fe28e22

[pre-commit.ci] auto fixes from pre-commit.com hooks

740c338

for more information, see https://pre-commit.ci

Fixup docs.

8361211

Update docs/extending.rst

0226f72

Pre-commit fixes

507c8c0

Partially fix doctest

470e995

Add test docstrings.

aa0c11f

Add typing_example tests

95b95d0

[pre-commit.ci] auto fixes from pre-commit.com hooks

ec4c7c0

for more information, see https://pre-commit.ci

Tidy typing_example

e2ed777

asford force-pushed the attrib_alias branch from b12c230 to e2ed777 Compare November 13, 2022 16:01

asford added 5 commits November 13, 2022 08:26

Add note in init.rst on private aliases

746f9ca

Add alias example to examples.rst

a80dfba

Assert to comment

859886f

Add changelog entry

5de8c67

Fixup doc error

f4879a7

asford mentioned this pull request Nov 13, 2022

Use Attribute.alias for init argument names if attrs>= 2022.2 python-attrs/cattrs#322

Closed

asford added 2 commits November 13, 2022 09:18

Tidy dataclass_transform docs

12bdbc5

Lil' spice for the changelog.

ce4746e

asford commented Nov 13, 2022

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asford requested a review from hynek November 13, 2022 17:28

asford and others added 4 commits November 13, 2022 09:33

Fix doctest

0f2879d

Update extending.rst

395b04c

Make alias introspection more explicit

cfa4eb7

Merge branch 'main' into attrib_alias

8685666

hynek mentioned this pull request Nov 28, 2022

Why strip leading underscores from attribute names? #1060

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Merge branch 'main' into attrib_alias

c3dd347

hynek approved these changes Nov 30, 2022

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hynek reviewed Nov 30, 2022

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Update src/attr/_make.py

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hynek enabled auto-merge (squash) November 30, 2022 14:36

hynek merged commit ee3ecb1 into python-attrs:main Nov 30, 2022

asford mentioned this pull request Nov 30, 2022

evolve() is broken if dunder attribute names are defined. #1062

Closed

querti mentioned this pull request Jan 5, 2023

Make pushsource compatible with attrs version 22.2.0 release-engineering/pushsource#295

Merged

hynek mentioned this pull request Apr 5, 2023

attr.ibs that will be __name-mangled should be attrs-init-mangled to <name> not ClassName_<name> #619

Open

Liam-DeVoe mentioned this pull request Dec 7, 2023

Support attrs alias and private attributes in st.builds HypothesisWorks/hypothesis#3807

Merged

side2k mentioned this pull request Feb 6, 2024

When using black from environment: AttributeError: 'Attribute' object has no attribute 'alias' microsoft/vscode-black-formatter#452

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asford commented Apr 9, 2022 •

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