attrs v20.1.0 Release NotesRelease Date: 2020-08-20 // about 2 years ago
- 👍 Python 3.4 is not supported anymore. It has been unsupported by the Python core team for a while now, its PyPI downloads are negligible, and our CI provider removed it as a supported option.
It's very unlikely that
attrswill break under 3.4 anytime soon, which is why we do not block its installation on Python 3.4. But we don't test it anymore and will block it once someone reports breakage.
🗄 Deprecations ^
- 🚀 Less of a deprecation and more of a heads up: the next release of
attrswill introduce an
attrsnamespace. That means that you'll finally be able to run
import attrswith new functions that aren't cute abbreviations and that will carry better defaults.
This should not break any of your code, because project-local packages have priority before installed ones. If this is a problem for you for some reason, please report it to our bug tracker and we'll figure something out.
attrnamespace isn't going anywhere and its defaults are not changing – this is a purely additive measure. Please check out the linked issue for more details.
These new APIs have been added provisionally as part of #666 so you can try them out today and provide feedback. Learn more in the
API docs <https://www.attrs.org/en/stable/api.html#provisional-apis>.
🔄 Changes ^
- ➕ Added
attr.resolve_types(). It ensures that all forward-references and types in string form are resolved into concrete types.
You need this only if you need concrete types at runtime. That means that if you only use types for static type checking, you do not need this function.
@attr.s(collect_by_mro=False)argument that if set to
Truefixes the collection of attributes from base classes.
It's only necessary for certain cases of multiple-inheritance but is kept off for now for backward-compatibility reasons. It will be turned on by default in the future.
As a side-effect,
attr.Attributenow always has an
inheritedattribute indicating whether an attribute on a class was directly defined or inherited.
- 📄 On Python 3, all generated methods now have a docstring explaining that they have been created by
- It is now possible to prevent
attrsfrom auto-generating the
__getstate__methods that are required for pickling of slotted classes.
@attr.s(auto_detect=True)and implement them yourself: if
attrsfinds either of the two methods directly on the decorated class, it assumes implicitly
getstate_setstate=False(and implements neither).
This option works with dict classes but should never be necessary.
- 🛠 Fixed a
ValueError: Cell is emptybug that could happen in some rare edge cases.
attrscan now automatically detect your own implementations and infer
hash=Falseif you set
attrswill ignore inherited methods. If the argument implies more than one method (e.g.
__ne__), it's enough for one of them to exist and
attrswill create neither.
This feature requires Python 3.
- ➕ Added
attr.converters.pipe(). The feature allows combining multiple conversion callbacks into one by piping the value through all of them, and retuning the last result.
As part of this feature, we had to relax the type information for converter callables.
- 🛠 Fixed serialization behavior of non-slots classes with
cache_hash=True. The hash cache will be cleared on operations which make "deep copies" of instances of classes with hash caching, though the cache will not be cleared with shallow copies like those made by
copy.deepcopy()or serialization and deserialization with
picklewould result in an un-initialized object.
This change also allows the creation of
cache_hash=Trueclasses with a custom
__setstate__, which was previously forbidden (
- It is now possible to specify hooks that are called whenever an attribute is set after a class has been instantiated.
You can pass
@attr.s()to set the default for all attributes on a class, and to
@attr.ib()to overwrite it for individual attributes.
attrsalso comes with a new module
attr.settersthat brings helpers that run validators, converters, or allow to freeze a subset of attributes.
- Provisional APIs called
attr.frozen()have been added.
They are only available on Python 3.6 and later, and call
attr.s()with different default values.
If nothing comes up, they will become the official way for creating classes in 20.2.0 (see above).
Please note that it may take some time until mypy – and other tools that have dedicated support for
attrs– recognize these new APIs. Please do not open issues on our bug tracker, there is nothing we can do about it.
- We have also provisionally added
attr.ib(). It also requires at least Python 3.6 and is keyword-only. Other than that, it only dropped a few arguments, but changed no defaults.
attr.ib()is not going anywhere.