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.. _api:
API
===
.. currentmodule:: attr
``attrs`` works by decorating a class using :func:`attr.s` and then optionally defining attributes on the class using :func:`attr.ib`.
.. note::
When this documentation speaks about "``attrs`` attributes" it means those attributes that are defined using :func:`attr.ib` in the class body.
What follows is the API explanation, if you'd like a more hands-on introduction, have a look at :doc:`examples`.
Core
----
.. autofunction:: attr.s(these=None, repr_ns=None, repr=True, cmp=True, hash=True, init=True, slots=False, frozen=False, str=False)
.. note::
``attrs`` also comes with a serious business alias ``attr.attrs``.
For example:
.. doctest::
>>> import attr
>>> @attr.s
... class C(object):
... _private = attr.ib()
>>> C(private=42)
C(_private=42)
>>> class D(object):
... def __init__(self, x):
... self.x = x
>>> D(1)
<D object at ...>
>>> D = attr.s(these={"x": attr.ib()}, init=False)(D)
>>> D(1)
D(x=1)
.. autofunction:: attr.ib
.. note::
``attrs`` also comes with a serious business alias ``attr.attrib``.
.. autoclass:: attr.Attribute
Instances of this class are frequently used for introspection purposes like:
- :func:`fields` returns a tuple of them.
- Validators get them passed as the first argument.
.. warning::
You should never instantiate this class yourself!
.. doctest::
>>> import attr
>>> @attr.s
... class C(object):
... x = attr.ib()
>>> C.x
Attribute(name='x', default=NOTHING, validator=None, repr=True, cmp=True, hash=True, init=True, convert=None, metadata=mappingproxy({}))
.. autofunction:: attr.make_class
This is handy if you want to programmatically create classes.
For example:
.. doctest::
>>> C1 = attr.make_class("C1", ["x", "y"])
>>> C1(1, 2)
C1(x=1, y=2)
>>> C2 = attr.make_class("C2", {"x": attr.ib(default=42),
... "y": attr.ib(default=attr.Factory(list))})
>>> C2()
C2(x=42, y=[])
.. autoclass:: attr.Factory
For example:
.. doctest::
>>> @attr.s
... class C(object):
... x = attr.ib(default=attr.Factory(list))
>>> C()
C(x=[])
.. autoexception:: attr.exceptions.FrozenInstanceError
.. autoexception:: attr.exceptions.AttrsAttributeNotFoundError
.. autoexception:: attr.exceptions.NotAnAttrsClassError
.. _helpers:
Helpers
-------
``attrs`` comes with a bunch of helper methods that make working with it easier:
.. autofunction:: attr.fields
For example:
.. doctest::
>>> @attr.s
... class C(object):
... x = attr.ib()
... y = attr.ib()
>>> attr.fields(C)
(Attribute(name='x', default=NOTHING, validator=None, repr=True, cmp=True, hash=True, init=True, convert=None, metadata=mappingproxy({})), Attribute(name='y', default=NOTHING, validator=None, repr=True, cmp=True, hash=True, init=True, convert=None, metadata=mappingproxy({})))
>>> attr.fields(C)[1]
Attribute(name='y', default=NOTHING, validator=None, repr=True, cmp=True, hash=True, init=True, convert=None, metadata=mappingproxy({}))
>>> attr.fields(C).y is attr.fields(C)[1]
True
.. autofunction:: attr.has
For example:
.. doctest::
>>> @attr.s
... class C(object):
... pass
>>> attr.has(C)
True
>>> attr.has(object)
False
.. autofunction:: attr.asdict
For example:
.. doctest::
>>> @attr.s
... class C(object):
... x = attr.ib()
... y = attr.ib()
>>> attr.asdict(C(1, C(2, 3)))
{'y': {'y': 3, 'x': 2}, 'x': 1}
.. autofunction:: attr.astuple
For example:
.. doctest::
>>> @attr.s
... class C(object):
... x = attr.ib()
... y = attr.ib()
>>> attr.astuple(C(1,2))
(1, 2)
``attrs`` includes some handy helpers for filtering:
.. autofunction:: attr.filters.include
.. autofunction:: attr.filters.exclude
See :ref:`asdict` for examples.
.. autofunction:: assoc
For example:
.. doctest::
>>> @attr.s
... class C(object):
... x = attr.ib()
... y = attr.ib()
>>> i1 = C(1, 2)
>>> i1
C(x=1, y=2)
>>> i2 = attr.assoc(i1, y=3)
>>> i2
C(x=1, y=3)
>>> i1 == i2
False
.. autofunction:: validate
For example:
.. doctest::
>>> @attr.s
... class C(object):
... x = attr.ib(validator=attr.validators.instance_of(int))
>>> i = C(1)
>>> i.x = "1"
>>> attr.validate(i)
Traceback (most recent call last):
...
TypeError: ("'x' must be <type 'int'> (got '1' that is a <type 'str'>).", Attribute(name='x', default=NOTHING, validator=<instance_of validator for type <type 'int'>>, repr=True, cmp=True, hash=True, init=True), <type 'int'>, '1')
Validators can be globally disabled if you want to run them only in development and tests but not in production because you fear their performance impact:
.. autofunction:: set_run_validators
.. autofunction:: get_run_validators
.. _api_validators:
Validators
----------
``attrs`` comes with some common validators in the ``attrs.validators`` module:
.. autofunction:: attr.validators.instance_of
For example:
.. doctest::
>>> @attr.s
... class C(object):
... x = attr.ib(validator=attr.validators.instance_of(int))
>>> C(42)
C(x=42)
>>> C("42")
Traceback (most recent call last):
...
TypeError: ("'x' must be <type 'int'> (got '42' that is a <type 'str'>).", Attribute(name='x', default=NOTHING, validator=<instance_of validator for type <type 'int'>>), <type 'int'>, '42')
>>> C(None)
Traceback (most recent call last):
...
TypeError: ("'x' must be <type 'int'> (got None that is a <type 'NoneType'>).", Attribute(name='x', default=NOTHING, validator=<instance_of validator for type <type 'int'>>, repr=True, cmp=True, hash=True, init=True), <type 'int'>, None)
.. autofunction:: attr.validators.provides
.. autofunction:: attr.validators.optional
For example:
.. doctest::
>>> @attr.s
... class C(object):
... x = attr.ib(validator=attr.validators.optional(attr.validators.instance_of(int)))
>>> C(42)
C(x=42)
>>> C("42")
Traceback (most recent call last):
...
TypeError: ("'x' must be <type 'int'> (got '42' that is a <type 'str'>).", Attribute(name='x', default=NOTHING, validator=<instance_of validator for type <type 'int'>>), <type 'int'>, '42')
>>> C(None)
C(x=None)
Deprecated APIs
---------------
The serious business aliases used to be called ``attr.attributes`` and ``attr.attr``.
There are no plans to remove them but they shouldn't be used in new code.
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