Yesterday's 21.1.0 has unfortunately two regressions that we're fixing with today's 21.2.0 release:
The new recursive mode for attr.evolve() broke some use cases.
attrs is not importable under Python 3.4 anymore. While 3.4 hasn't been supported for a while now, we don't want it throw errors after installation.
We've reverted the changes to attr.evolve() and added packaging metadata blocking Python 3.4.
Additionally, we are yanking 21.1.0 from PyPI. If you've pinned attrs to 21.1.0, this does not affect you in any way.
21.1.0
I am extremely excited to announce the release of attrs 21.1.0.
attrs is the direct ancestor of – and the inspiration for – dataclasses in the standard library and remains the more powerful option for creating regular classes without getting bogged down with writing identical boilerplate again and again: https://www.attrs.org/
Heartfelt thanks go to my generous GitHub sponsors, companies subscribing to attrs on Tidelift, and people who bought me a coffee on Ko-fi! Support like that makes me work on FOSS on a Saturday afternoon – especially when a release drags itself like this one! <3
While this release took a bit longer than I wished for, it comes with many exciting changes. The highlights alone are longer than a usual changelog:
The next-generation APIs (@attr.define, @attr.mutable, @attr.frozen, @attr.field) are deemed stable now. The old ones aren't going anywhere, but I encourage you to check the new ones out – they're much nicer!
pyright and pylance support: Eric Traut of Microsoft was kind enough to involve me in their work on the dataclass_transforms spec.
As a result, Microsoft's type checker pyright will work with this attrs release, and so will their Python language server pylance which should be exciting to VS Code users.
Currently it only supports a subset of attrs's features, but it's the most important ones and more will most likely follow. Some of the limitations are documented in our documentation on type annotations.
Customization of field comparison. This is something especially NumPy users have been asking for for a long time: you can now fully customize how a field is compared. We also ship a helper to avoid boilerplate code. So if you'd like to have an object with a NumPy array that compares correctly, this is the way:
import attr
import numpy
@attr.define
class C:
an_array = attr.field(eq=attr.cmp_using(eq=numpy.array_equal))
To make it more ergonomic, I've decided to un-deprecate the cmp argument again, so you can customize eq and order in one go. Sorry about the trouble! The cmpattribute remains deprecated.
New powerful __init__ helpers:
If attrs deduces you don't want it to write a __init__ for you, it will create an __attrs_init__ instead that you can call from your custom __init__.
If attrs finds a __attrs_pre_init__, it will call it without any arguments before doing any initializations. This is really only useful if you want to run super().__init__(), but that's a use-case people have asked for for years!
In preparation for the (rescinded) plan to make from __future__ import annotations the default in Python 3.10, attr.resolve_types() can now also be used to resolve types inside of field_transformers.
A Look Ahead
For the next release we've got even bigger plans! By stabilizing the next-generation APIs we can finally go the last step, I've been talking for years (yeah, sorry): import attrs.
We had to revert the recursive feature for attr.evolve() because it broke some use-cases -- sorry! #806
Python 3.4 is now blocked using packaging metadata because attrs can't be imported on it anymore. To ensure that 3.4 users can keep installing attrs easily, we will yank 21.1.0 from PyPI. This has no consequences if you pin attrs to 21.1.0. #807
21.1.0 (2021-05-06)
Deprecations
The long-awaited, much-talked-about, little-delivered import attrs is finally upon us!
Since the NG APIs have now been proclaimed stable, the next release of attrs will allow you to actually import attrs. We're taking this opportunity to replace some defaults in our APIs that made sense in 2015, but don't in 2021.
So please, if you have any pet peeves about defaults in attrs's APIs, now is the time to air your grievances in #487! We're not gonna get such a chance for a second time, without breaking our backward-compatibility guarantees, or long deprecation cycles. Therefore, speak now or forever hold you peace! #487
The cmp argument to attr.s() and attr.ib() has been undeprecated It will continue to be supported as syntactic sugar to set eq and order in one go.
I'm terribly sorry for the hassle around this argument! The reason we're bringing it back is it's usefulness regarding customization of equality/ordering.
The cmp attribute and argument on attr.Attribute remains deprecated and will be removed later this year. #773
Changes
It's now possible to customize the behavior of eq and order by passing in a callable. #435, #627
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Bumps attrs from 19.3.0 to 21.2.0.
Release notes
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Changelog
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Commits
83d3cd7
Prepare 21.2.0f83dabb
That comma is not necessary744a790
Clarify yanking of 21.18076287
Create 807.breaking.rst966c220
Declare Python 3.4 as incompatible (#807)f10d050
Revert recursive evolve (#806)24a2c1e
Start new cycleb22195e
Prepare 21.1.0c5ae43f
Pin towncrier503164f
Fix changelog template for towncrier 21.3.0Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting
@dependabot rebase
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