Versions follow CalVer with a strict backwards compatibility policy. The third digit is only for regressions.
Changes for the upcoming release can be found in the “changelog.d” directory in our repository.
__ge__do not consider subclasses comparable anymore.
This has been deprecated since 18.2.0 and was raising a
DeprecationWarningfor over a year. #570
attr.ib()is now deprecated.
eqto add equality methods (
orderto add ordering methods (
__ge__) instead – just like with dataclasses.
Both are effectively
Trueby default but it’s enough to set
eq=Falseto disable both at once. Passing
eq=False, order=Trueexplicitly will raise a
Since this is arguably a deeper backward-compatibility break, it will have an extended deprecation period until 2021-06-01. After that day, the
cmpargument will be removed.
attr.Attributealso isn’t orderable anymore. #574
Slotted classes now use a pure Python mechanism to rewrite the
__class__cell when rebuilding the class, so
super()works even on environments where
ctypesis not installed. #522
attr.validators.deep_mapping()type stubs. #533
attr.validators.is_callable()validator now raises an exception
attr.exceptions.NotCallableError, a subclass of
TypeError, informing the received value. #536
attr.validators.matches_re()that checks string attributes whether they match a regular expression. #552
Keyword-only attributes (
kw_only=True) and attributes that are excluded from the
init=False) now can appear before mandatory attributes. #559
The fake filename for generated methods is now more stable. It won’t change when you restart the process. #560
The value passed to
@attr.ib(repr=…)can now be either a boolean (as before) or a callable. That callable must return a string and is then used for formatting the attribute by the generated
attr.__version_info__that can be used to reliably check the version of
attrsand write forward- and backward-compatible code. Please check out the section on deprecated APIs on how to use it. #580
Fixed a bug where deserialized objects with
cache_hash=Truecould have incorrect hash code values. This change breaks classes with
cache_hash=Truewhen a custom
__setstate__is present. An exception will be thrown when applying the
attrsannotation to such a class. This limitation is tracked in issue #494. #482
is_callable: validates that a value is callable
deep_iterable: Allows recursion down into an iterable, applying another validator to every member in the iterable as well as applying an optional validator to the iterable itself.
deep_mapping: Allows recursion down into the items in a mapping object, applying a key validator and a value validator to the key and value in every item. Also applies an optional validator to the mapping object itself.
You can find them in the
Fixed stub files to prevent errors raised by mypy’s
disallow_any_generics = Trueoption. #443
init=Falsenow can follow after
attrsnow has first class support for defining exception classes.
If you define a class using
@attr.s(auto_exc=True)and subclass an exception, the class will behave like a well-behaved exception class including an appropriate
__str__method, and all attributes additionally available in an
Clarified documentation for hashing to warn that hashable objects should be deeply immutable (in their usage, even if this is not enforced). #503
Comparing subclasses using
>=is now deprecated. The docs always claimed that instances are only compared if the types are identical, so this is a first step to conform to the docs.
Equality operators (
!=) were always strict in this regard. #394
Added kw_only arguments to
attr.s, and a corresponding kw_only attribute to
attr.Attribute. This change makes it possible to have a generated
__init__with keyword-only arguments on Python 3, relaxing the required ordering of default and non-default valued attributes. #281, #411
attr.validators.in_()now raises a
ValueErrorwith a useful message even if the options are a string and the value is not a string. #383
attr.asdict()now properly handles deeply nested lists and dictionaries. #395
Fixed a reference leak where the original class would remain live after being replaced when
slots=Trueis set. #407
Slotted classes can now be made weakly referenceable by passing
Added cache_hash option to
@attr.swhich causes the hash code to be computed once and stored on the object. #426
Attributes can be named
It is now possible to override a base class’ class variable using only class annotations. #431
x=X(); x.cycle = x; repr(x)will no longer raise a
RecursionError, and will instead show as
attr.ib(factory=f)is now syntactic sugar for the common case of
attr.field_dict()to return an ordered dictionary of
attrsattributes for a class, whose keys are the attribute names.
The order of attributes that are passed into
attr.make_class()or the these argument of
@attr.s()is now retained if the dictionary is ordered (i.e.
dicton Python 3.6 and later,
Before, the order was always determined by the order in which the attributes have been defined which may not be desirable when creating classes programatically.
In slotted classes,
__setstate__now ignore the
Setting the cell type is now completely best effort. This fixes
We cannot make any guarantees regarding Jython though, because our test suite cannot run due to dependency incompatabilities.
attr.sis passed a these argument, it will no longer attempt to remove attributes with the same name from the class body.
The hash of
attr.NOTHINGis now vegan and faster on 32bit Python builds.
The overhead of instantiating frozen dict classes is virtually eliminated. #336
__init__methods now have an
__annotations__attribute derived from the types of the fields.
We have restructured the documentation a bit to account for
attrs’ growth in scope. Instead of putting everything into the examples page, we have started to extract narrative chapters.
Expect more to come!
The traversal of MROs when using multiple inheritance was backward: If you defined a class
attrswould have collected the attributes from
Bbefore those of
This is now fixed and means that in classes that employ multiple inheritance, the output of
__repr__and the order of positional arguments in
__init__changes. Because of the nature of this bug, a proper deprecation cycle was unfortunately impossible.
Generally speaking, it’s advisable to prefer
kwargs-based initialization anyways – especially if you employ multiple inheritance and diamond-shaped hierarchies.
attrsno longer produces an
AttributeErrorwhen the instance is missing some of the specified attributes (either through deleting or after using
init=Falseon some attributes).
This can break code that relied on
AttributeErrorto check if any
attrs-specified members were unset.
If you were using this, you can implement a custom method for checking this:
def has_unset_members(self): for field in attr.fields(type(self)): try: getattr(self, field.name) except AttributeError: return True return False
attr.ib(convert=callable)option is now deprecated in favor of
This is done to achieve consistency with other noun-based arguments like validator.
convert will keep working until at least January 2019 while raising a
__hash__methods now hash the class type along with the attribute values. Until now the hashes of two classes with the same values were identical which was a bug.
The generated method is also much faster now.
attr.ib’s metadata argument now defaults to a unique empty
dictinstance instead of sharing a common empty
dictfor all. The singleton empty
dictis still enforced.
ctypesis optional now however if it’s missing, a bare
super()will not work in slotted classes. This should only happen in special environments like Google App Engine.
The attribute redefinition feature introduced in 17.3.0 now takes into account if an attribute is redefined via multiple inheritance. In that case, the definition that is closer to the base of the class hierarchy wins.
auto_attribs=Truecan be empty now.
Equality tests are much faster now.
All generated methods now have correct
__name__, and (on Python 3)
Attributes are no longer defined on the class body.
This means that if you define a class
Cwith an attribute
x, the class will not have an attribute
xfor introspection. Instead of
attr.fields(C).xor look at
C.__attrs_attrs__. The old behavior has been deprecated since version 16.1. (#253)
Added type argument to
This change paves the way for automatic type checking and serialization (though as of this release
attrsdoes not make use of it). In Python 3.6 or higher, the value of
attr.Attribute.typecan alternately be set using variable type annotations (see PEP 526). (#151, #214, #215, #239)
The combination of
slots=Truenow works on Python 2. (#198)
attr.Factoryis hashable again. (#204)
Subclasses now can overwrite attribute definitions of their base classes.
Added new option auto_attribs to
@attr.sthat allows to collect annotated fields without setting them to
Setting a field to an
attr.ib()is still possible to supply options like validators. Setting it to any other value is treated like it was passed as
attr.ib(default=value)– passing an instance of
attr.Factoryalso works as expected. (#262, #277)
Instances of classes created using
attr.make_class()can now be pickled. (#282)
To encourage more participation, the project has also been moved into a dedicated GitHub organization and everyone is most welcome to join!
attrs also has a logo now!
attrswill set the
Noneby default now. The way hashes were handled before was in conflict with Python’s specification. This may break some software although this breakage is most likely just surfacing of latent bugs. You can always make
@attr.s(hash=True). See #136 for the rationale of this change.
Please do not upgrade blindly and do test your software! Especially if you use instances as dict keys or put them into sets!
attr.ib’s hash argument is
Noneby default too and mirrors the cmp argument as it should.
attr.assoc()is now deprecated in favor of
attr.evolve()and will stop working in 2018.
attr.evolve()that, given an instance of an
attrsclass and field changes as keyword arguments, will instantiate a copy of the given instance with the changes applied.
assoc(), which is now deprecated.
evolve()is significantly faster than
assoc(), and requires the class have an initializer that can take the field values as keyword arguments (like
attrsitself can generate). #116 #124 #135
FrozenInstanceErroris now raised when trying to delete an attribute from a frozen class. #118
Frozen-ness of classes is now inherited. #128
__attrs_post_init__()is now run if validation is disabled. #130
attr.validators.in_(options)that, given the allowed
options, checks whether the attribute value is in it. This can be used to check constants, enums, mappings, etc. #181
attr.validators.and_()that composes multiple validators into one. #161
For convenience, the validator argument of
@attr.snow can take a list of validators that are wrapped using
attr.validators.optional()now can take a list of validators too. #161
attr.Factory()now has a takes_self argument that makes the initializer to pass the partially initialized instance into the factory. In other words you can define attribute defaults based on other attributes. #165 #189
Default factories can now also be defined inline using decorators. They are always passed the partially initialized instance. #165
attr.make_class()now accepts the keyword argument
baseswhich allows for subclassing. #152
Metaclasses are now preserved with
Attributes now can have user-defined metadata which greatly improves
attrs’s extensibility. #96
Allow for a
__attrs_post_init__()method that – if defined – will get called at the end of the
@attr.s(str=True)that will optionally create a
__str__()method that is identical to
__repr__(). This is mainly useful with
Exceptions and other classes that rely on a useful
__str__()implementation but overwrite the default one through a poor own one. Default Python class behavior is to use
If you tried using
Exceptions and were puzzled by the tracebacks: this option is for you.
__name__is no longer overwritten with
attr.astuple()that – similarly to
attr.asdict()– returns the instance as a tuple. #77
Converters now work with frozen classes. #76
attrsclasses with converters is now significantly faster. #80
Pickling now works with slotted classes. #81
attr.assoc()now works with slotted classes. #84
The tuple returned by
attr.fields()now also allows to access the
Attributeinstances by name. Yes, we’ve subclassed
tupleso you don’t have to! Therefore
attr.fields(C).xis equivalent to the deprecated
C.xand works with slotted classes. #88
All instances where function arguments were called
clhave been changed to the more Pythonic
cls. Since it was always the first argument, it’s doubtful anyone ever called those function with in the keyword form. If so, sorry for any breakage but there’s no practical deprecation path to solve this ugly wart.
Attributeinstances on class objects is now deprecated and will stop working in 2017. If you need introspection please use the
__attrs_attrs__attribute or the
attr.fields()function that carry them too. In the future, the attributes that are defined on the class body and are usually overwritten in your
__init__method are simply removed after
@attr.shas been applied.
This will remove the confusing error message if you write your own
__init__and forget to initialize some attribute. Instead you will get a straightforward
AttributeError. In other words: decorated classes will work more like plain Python classes which was always
The serious business aliases
attr.attrhave been deprecated in favor of
attr.attribwhich are much more consistent and frankly obvious in hindsight. They will be purged from documentation immediately but there are no plans to actually remove them.
dict_factoryarguments is now propagated on recursion. #45
attr.attribas a more consistent aliases for
Add frozen option to
attr.sthat will make instances best-effort immutable. #60
retain_collection_typesas an argument. If
True, it does not convert attributes of type
Python 3.3 and 2.6 are no longer supported. They may work by chance but any effort to keep them working has ceased.
The last Python 2.6 release was on October 29, 2013 and is no longer supported by the CPython core team. Major Python packages like Django and Twisted dropped Python 2.6 a while ago already.
Python 3.3 never had a significant user base and wasn’t part of any distribution’s LTS release.
Allow the case of initializing attributes that are set to
init=False. This allows for clean initializer parameter lists while being able to initialize attributes to default values. #32
attr.asdict()can now produce arbitrary mappings instead of Python
dicts when provided with a
Multiple performance improvements.