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Add Attribute.alias #950

Merged
merged 24 commits into from Nov 30, 2022
Merged

Add Attribute.alias #950

merged 24 commits into from Nov 30, 2022

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asford
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@asford asford commented Apr 9, 2022

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

  • Added tests for changed code.
    Our CI fails if coverage is not 100%.
  • New features have been added to our Hypothesis testing strategy.
  • Changes or additions to public APIs are reflected in our type stubs (files ending in .pyi).
    • ...and used in the stub test file tests/typing_example.py.
    • If they've been added to attr/__init__.pyi, they've also been re-imported in attrs/__init__.pyi.
  • Updated documentation for changed code.
    • New functions/classes have to be added to docs/api.rst by hand.
    • Changes to the signature of @attr.s() have to be added by hand too.
    • Changed/added classes/methods/functions have appropriate versionadded, versionchanged, or deprecated directives.
      Find the appropriate next version in our __init__.py file.
  • Documentation in .rst files is written using semantic newlines.
  • Changes (and possible deprecations) have news fragments in changelog.d.
  • Consider granting push permissions to the PR branch, so maintainers can fix minor issues themselves without pestering you.

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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.

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hynek commented May 25, 2022

Anything you need from my end? 😇

@hynek hynek added this to the 22.2.0 milestone Aug 11, 2022
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My turn to apologize for the slow turnaround.

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

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@asford asford requested a review from hynek November 13, 2022 17:28
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hynek commented Nov 16, 2022

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

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asford commented Nov 16, 2022

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

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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.

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@hynek hynek enabled auto-merge (squash) November 30, 2022 14:36
@hynek hynek merged commit ee3ecb1 into python-attrs:main Nov 30, 2022
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Tinche commented Nov 30, 2022

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.

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hynek commented Nov 30, 2022

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

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Tinche commented Nov 30, 2022

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

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hynek commented Nov 30, 2022

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 🐶🥺?

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Tinche commented Nov 30, 2022

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

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hynek commented Nov 30, 2022

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.

querti added a commit to querti/pushsource that referenced this pull request Jan 5, 2023
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
querti added a commit to querti/pushsource that referenced this pull request Jan 5, 2023
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
querti added a commit to querti/pushsource that referenced this pull request Jan 5, 2023
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
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