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Help on package attr: NAME attr - Classes Without Boilerplate <https://www.attrs.org/> PACKAGE CONTENTS _cmp _compat _config _funcs _make _next_gen _version_info converters exceptions filters setters validators CLASSES builtins.object attr._make.Attribute attr._make.Factory class Attribute(builtins.object) | Attribute(name, default, validator, repr, cmp, hash, init, inherited, metadata=None, type=None, converter=None, kw_only=False, eq=None, eq_key=None, order=None, order_key=None, on_setattr=None) | | *Read-only* representation of an attribute. | | Instances of this class are frequently used for introspection purposes | like: | | - `fields` returns a tuple of them. | - Validators get them passed as the first argument. | - The *field transformer* hook receives a list of them. | | :attribute name: The name of the attribute. | :attribute inherited: Whether or not that attribute has been inherited from | a base class. | | Plus *all* arguments of `attr.ib` (except for ``factory`` | which is only syntactic sugar for ``default=Factory(...)``. | | .. versionadded:: 20.1.0 *inherited* | .. versionadded:: 20.1.0 *on_setattr* | .. versionchanged:: 20.2.0 *inherited* is not taken into account for | equality checks and hashing anymore. | .. versionadded:: 21.1.0 *eq_key* and *order_key* | | For the full version history of the fields, see `attr.ib`. | | Methods defined here: | | __eq__(self, other) | | __getstate__(self) | Play nice with pickle. | | __hash__(self) | | __init__(self, name, default, validator, repr, cmp, hash, init, inherited, metadata=None, type=None, converter=None, kw_only=False, eq=None, eq_key=None, order=None, order_key=None, on_setattr=None) | Initialize self. See help(type(self)) for accurate signature. | | __ne__(self, other) | Check equality and either forward a NotImplemented or | return the result negated. | | __repr__(self) | Automatically created by attrs. | | __setattr__(self, name, value) | Implement setattr(self, name, value). | | __setstate__(self, state) | Play nice with pickle. | | evolve(self, **changes) | Copy *self* and apply *changes*. | | This works similarly to `attr.evolve` but that function does not work | with ``Attribute``. | | It is mainly meant to be used for `transform-fields`. | | .. versionadded:: 20.3.0 | | ---------------------------------------------------------------------- | Class methods defined here: | | from_counting_attr(name, ca, type=None) from builtins.type | | ---------------------------------------------------------------------- | Readonly properties defined here: | | cmp | Simulate the presence of a cmp attribute and warn. | | ---------------------------------------------------------------------- | Data descriptors defined here: | | converter | | default | | eq | | eq_key | | hash | | inherited | | init | | kw_only | | metadata | | name | | on_setattr | | order | | order_key | | repr | | type | | validator class Factory(builtins.object) | Factory(factory, takes_self=False) | | Stores a factory callable. | | If passed as the default value to `attr.ib`, the factory is used to | generate a new value. | | :param callable factory: A callable that takes either none or exactly one | mandatory positional argument depending on *takes_self*. | :param bool takes_self: Pass the partially initialized instance that is | being initialized as a positional argument. | | .. versionadded:: 17.1.0 *takes_self* | | Methods defined here: | | __eq__(self, other) | | __getstate__(self) | Play nice with pickle. | | __hash__(self) | | __init__(self, factory, takes_self=False) | `Factory` is part of the default machinery so if we want a default | value here, we have to implement it ourselves. | | __ne__(self, other) | Check equality and either forward a NotImplemented or | return the result negated. | | __repr__(self) | Automatically created by attrs. | | __setstate__(self, state) | Play nice with pickle. | | ---------------------------------------------------------------------- | Data descriptors defined here: | | factory | | takes_self FUNCTIONS asdict(inst, recurse=True, filter=None, dict_factory=<class 'dict'>, retain_collection_types=False, value_serializer=None) Return the ``attrs`` attribute values of *inst* as a dict. Optionally recurse into other ``attrs``-decorated classes. :param inst: Instance of an ``attrs``-decorated class. :param bool recurse: Recurse into classes that are also ``attrs``-decorated. :param callable filter: A callable whose return code determines whether an attribute or element is included (``True``) or dropped (``False``). Is called with the `attr.Attribute` as the first argument and the value as the second argument. :param callable dict_factory: A callable to produce dictionaries from. For example, to produce ordered dictionaries instead of normal Python dictionaries, pass in ``collections.OrderedDict``. :param bool retain_collection_types: Do not convert to ``list`` when encountering an attribute whose type is ``tuple`` or ``set``. Only meaningful if ``recurse`` is ``True``. :param Optional[callable] value_serializer: A hook that is called for every attribute or dict key/value. It receives the current instance, field and value and must return the (updated) value. The hook is run *after* the optional *filter* has been applied. :rtype: return type of *dict_factory* :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs`` class. .. versionadded:: 16.0.0 *dict_factory* .. versionadded:: 16.1.0 *retain_collection_types* .. versionadded:: 20.3.0 *value_serializer* assoc(inst, **changes) Copy *inst* and apply *changes*. :param inst: Instance of a class with ``attrs`` attributes. :param changes: Keyword changes in the new copy. :return: A copy of inst with *changes* incorporated. :raise attr.exceptions.AttrsAttributeNotFoundError: If *attr_name* couldn't be found on *cls*. :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs`` class. .. deprecated:: 17.1.0 Use `evolve` instead. astuple(inst, recurse=True, filter=None, tuple_factory=<class 'tuple'>, retain_collection_types=False) Return the ``attrs`` attribute values of *inst* as a tuple. Optionally recurse into other ``attrs``-decorated classes. :param inst: Instance of an ``attrs``-decorated class. :param bool recurse: Recurse into classes that are also ``attrs``-decorated. :param callable filter: A callable whose return code determines whether an attribute or element is included (``True``) or dropped (``False``). Is called with the `attr.Attribute` as the first argument and the value as the second argument. :param callable tuple_factory: A callable to produce tuples from. For example, to produce lists instead of tuples. :param bool retain_collection_types: Do not convert to ``list`` or ``dict`` when encountering an attribute which type is ``tuple``, ``dict`` or ``set``. Only meaningful if ``recurse`` is ``True``. :rtype: return type of *tuple_factory* :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs`` class. .. versionadded:: 16.2.0 attr = attrib(default=NOTHING, validator=None, repr=True, cmp=None, hash=None, init=True, metadata=None, type=None, converter=None, factory=None, kw_only=False, eq=None, order=None, on_setattr=None) Create a new attribute on a class. .. warning:: Does *not* do anything unless the class is also decorated with `attr.s`! :param default: A value that is used if an ``attrs``-generated ``__init__`` is used and no value is passed while instantiating or the attribute is excluded using ``init=False``. If the value is an instance of `Factory`, its callable will be used to construct a new value (useful for mutable data types like lists or dicts). If a default is not set (or set manually to `attr.NOTHING`), a value *must* be supplied when instantiating; otherwise a `TypeError` will be raised. The default can also be set using decorator notation as shown below. :type default: Any value :param callable factory: Syntactic sugar for ``default=attr.Factory(factory)``. :param validator: `callable` that is called by ``attrs``-generated ``__init__`` methods after the instance has been initialized. They receive the initialized instance, the `Attribute`, and the passed value. The return value is *not* inspected so the validator has to throw an exception itself. If a `list` is passed, its items are treated as validators and must all pass. Validators can be globally disabled and re-enabled using `get_run_validators`. The validator can also be set using decorator notation as shown below. :type validator: `callable` or a `list` of `callable`\ s. :param repr: Include this attribute in the generated ``__repr__`` method. If ``True``, include the attribute; if ``False``, omit it. By default, the built-in ``repr()`` function is used. To override how the attribute value is formatted, pass a ``callable`` that takes a single value and returns a string. Note that the resulting string is used as-is, i.e. it will be used directly *instead* of calling ``repr()`` (the default). :type repr: a `bool` or a `callable` to use a custom function. :param eq: If ``True`` (default), include this attribute in the generated ``__eq__`` and ``__ne__`` methods that check two instances for equality. To override how the attribute value is compared, pass a ``callable`` that takes a single value and returns the value to be compared. :type eq: a `bool` or a `callable`. :param order: If ``True`` (default), include this attributes in the generated ``__lt__``, ``__le__``, ``__gt__`` and ``__ge__`` methods. To override how the attribute value is ordered, pass a ``callable`` that takes a single value and returns the value to be ordered. :type order: a `bool` or a `callable`. :param cmp: Setting *cmp* is equivalent to setting *eq* and *order* to the same value. Must not be mixed with *eq* or *order*. :type cmp: a `bool` or a `callable`. :param Optional[bool] hash: Include this attribute in the generated ``__hash__`` method. If ``None`` (default), mirror *eq*'s value. This is the correct behavior according the Python spec. Setting this value to anything else than ``None`` is *discouraged*. :param bool init: Include this attribute in the generated ``__init__`` method. It is possible to set this to ``False`` and set a default value. In that case this attributed is unconditionally initialized with the specified default value or factory. :param callable converter: `callable` that is called by ``attrs``-generated ``__init__`` methods to convert attribute's value to the desired format. It is given the passed-in value, and the returned value will be used as the new value of the attribute. The value is converted before being passed to the validator, if any. :param metadata: An arbitrary mapping, to be used by third-party components. See `extending_metadata`. :param type: The type of the attribute. In Python 3.6 or greater, the preferred method to specify the type is using a variable annotation (see `PEP 526 <https://www.python.org/dev/peps/pep-0526/>`_). This argument is provided for backward compatibility. Regardless of the approach used, the type will be stored on ``Attribute.type``. Please note that ``attrs`` doesn't do anything with this metadata by itself. You can use it as part of your own code or for `static type checking <types>`. :param kw_only: Make this attribute keyword-only (Python 3+) in the generated ``__init__`` (if ``init`` is ``False``, this parameter is ignored). :param on_setattr: Allows to overwrite the *on_setattr* setting from `attr.s`. If left `None`, the *on_setattr* value from `attr.s` is used. Set to `attr.setters.NO_OP` to run **no** `setattr` hooks for this attribute -- regardless of the setting in `attr.s`. :type on_setattr: `callable`, or a list of callables, or `None`, or `attr.setters.NO_OP` .. versionadded:: 15.2.0 *convert* .. versionadded:: 16.3.0 *metadata* .. versionchanged:: 17.1.0 *validator* can be a ``list`` now. .. versionchanged:: 17.1.0 *hash* is ``None`` and therefore mirrors *eq* by default. .. versionadded:: 17.3.0 *type* .. deprecated:: 17.4.0 *convert* .. versionadded:: 17.4.0 *converter* as a replacement for the deprecated *convert* to achieve consistency with other noun-based arguments. .. versionadded:: 18.1.0 ``factory=f`` is syntactic sugar for ``default=attr.Factory(f)``. .. versionadded:: 18.2.0 *kw_only* .. versionchanged:: 19.2.0 *convert* keyword argument removed. .. versionchanged:: 19.2.0 *repr* also accepts a custom callable. .. deprecated:: 19.2.0 *cmp* Removal on or after 2021-06-01. .. versionadded:: 19.2.0 *eq* and *order* .. versionadded:: 20.1.0 *on_setattr* .. versionchanged:: 20.3.0 *kw_only* backported to Python 2 .. versionchanged:: 21.1.0 *eq*, *order*, and *cmp* also accept a custom callable .. versionchanged:: 21.1.0 *cmp* undeprecated attrib(default=NOTHING, validator=None, repr=True, cmp=None, hash=None, init=True, metadata=None, type=None, converter=None, factory=None, kw_only=False, eq=None, order=None, on_setattr=None) Create a new attribute on a class. .. warning:: Does *not* do anything unless the class is also decorated with `attr.s`! :param default: A value that is used if an ``attrs``-generated ``__init__`` is used and no value is passed while instantiating or the attribute is excluded using ``init=False``. If the value is an instance of `Factory`, its callable will be used to construct a new value (useful for mutable data types like lists or dicts). If a default is not set (or set manually to `attr.NOTHING`), a value *must* be supplied when instantiating; otherwise a `TypeError` will be raised. The default can also be set using decorator notation as shown below. :type default: Any value :param callable factory: Syntactic sugar for ``default=attr.Factory(factory)``. :param validator: `callable` that is called by ``attrs``-generated ``__init__`` methods after the instance has been initialized. They receive the initialized instance, the `Attribute`, and the passed value. The return value is *not* inspected so the validator has to throw an exception itself. If a `list` is passed, its items are treated as validators and must all pass. Validators can be globally disabled and re-enabled using `get_run_validators`. The validator can also be set using decorator notation as shown below. :type validator: `callable` or a `list` of `callable`\ s. :param repr: Include this attribute in the generated ``__repr__`` method. If ``True``, include the attribute; if ``False``, omit it. By default, the built-in ``repr()`` function is used. To override how the attribute value is formatted, pass a ``callable`` that takes a single value and returns a string. Note that the resulting string is used as-is, i.e. it will be used directly *instead* of calling ``repr()`` (the default). :type repr: a `bool` or a `callable` to use a custom function. :param eq: If ``True`` (default), include this attribute in the generated ``__eq__`` and ``__ne__`` methods that check two instances for equality. To override how the attribute value is compared, pass a ``callable`` that takes a single value and returns the value to be compared. :type eq: a `bool` or a `callable`. :param order: If ``True`` (default), include this attributes in the generated ``__lt__``, ``__le__``, ``__gt__`` and ``__ge__`` methods. To override how the attribute value is ordered, pass a ``callable`` that takes a single value and returns the value to be ordered. :type order: a `bool` or a `callable`. :param cmp: Setting *cmp* is equivalent to setting *eq* and *order* to the same value. Must not be mixed with *eq* or *order*. :type cmp: a `bool` or a `callable`. :param Optional[bool] hash: Include this attribute in the generated ``__hash__`` method. If ``None`` (default), mirror *eq*'s value. This is the correct behavior according the Python spec. Setting this value to anything else than ``None`` is *discouraged*. :param bool init: Include this attribute in the generated ``__init__`` method. It is possible to set this to ``False`` and set a default value. In that case this attributed is unconditionally initialized with the specified default value or factory. :param callable converter: `callable` that is called by ``attrs``-generated ``__init__`` methods to convert attribute's value to the desired format. It is given the passed-in value, and the returned value will be used as the new value of the attribute. The value is converted before being passed to the validator, if any. :param metadata: An arbitrary mapping, to be used by third-party components. See `extending_metadata`. :param type: The type of the attribute. In Python 3.6 or greater, the preferred method to specify the type is using a variable annotation (see `PEP 526 <https://www.python.org/dev/peps/pep-0526/>`_). This argument is provided for backward compatibility. Regardless of the approach used, the type will be stored on ``Attribute.type``. Please note that ``attrs`` doesn't do anything with this metadata by itself. You can use it as part of your own code or for `static type checking <types>`. :param kw_only: Make this attribute keyword-only (Python 3+) in the generated ``__init__`` (if ``init`` is ``False``, this parameter is ignored). :param on_setattr: Allows to overwrite the *on_setattr* setting from `attr.s`. If left `None`, the *on_setattr* value from `attr.s` is used. Set to `attr.setters.NO_OP` to run **no** `setattr` hooks for this attribute -- regardless of the setting in `attr.s`. :type on_setattr: `callable`, or a list of callables, or `None`, or `attr.setters.NO_OP` .. versionadded:: 15.2.0 *convert* .. versionadded:: 16.3.0 *metadata* .. versionchanged:: 17.1.0 *validator* can be a ``list`` now. .. versionchanged:: 17.1.0 *hash* is ``None`` and therefore mirrors *eq* by default. .. versionadded:: 17.3.0 *type* .. deprecated:: 17.4.0 *convert* .. versionadded:: 17.4.0 *converter* as a replacement for the deprecated *convert* to achieve consistency with other noun-based arguments. .. versionadded:: 18.1.0 ``factory=f`` is syntactic sugar for ``default=attr.Factory(f)``. .. versionadded:: 18.2.0 *kw_only* .. versionchanged:: 19.2.0 *convert* keyword argument removed. .. versionchanged:: 19.2.0 *repr* also accepts a custom callable. .. deprecated:: 19.2.0 *cmp* Removal on or after 2021-06-01. .. versionadded:: 19.2.0 *eq* and *order* .. versionadded:: 20.1.0 *on_setattr* .. versionchanged:: 20.3.0 *kw_only* backported to Python 2 .. versionchanged:: 21.1.0 *eq*, *order*, and *cmp* also accept a custom callable .. versionchanged:: 21.1.0 *cmp* undeprecated attributes = attrs(maybe_cls=None, these=None, repr_ns=None, repr=None, cmp=None, hash=None, init=None, slots=False, frozen=False, weakref_slot=True, str=False, auto_attribs=False, kw_only=False, cache_hash=False, auto_exc=False, eq=None, order=None, auto_detect=False, collect_by_mro=False, getstate_setstate=None, on_setattr=None, field_transformer=None) A class decorator that adds `dunder <https://wiki.python.org/moin/DunderAlias>`_\ -methods according to the specified attributes using `attr.ib` or the *these* argument. :param these: A dictionary of name to `attr.ib` mappings. This is useful to avoid the definition of your attributes within the class body because you can't (e.g. if you want to add ``__repr__`` methods to Django models) or don't want to. If *these* is not ``None``, ``attrs`` will *not* search the class body for attributes and will *not* remove any attributes from it. If *these* is an ordered dict (`dict` on Python 3.6+, `collections.OrderedDict` otherwise), the order is deduced from the order of the attributes inside *these*. Otherwise the order of the definition of the attributes is used. :type these: `dict` of `str` to `attr.ib` :param str repr_ns: When using nested classes, there's no way in Python 2 to automatically detect that. Therefore it's possible to set the namespace explicitly for a more meaningful ``repr`` output. :param bool auto_detect: Instead of setting the *init*, *repr*, *eq*, *order*, and *hash* arguments explicitly, assume they are set to ``True`` **unless any** of the involved methods for one of the arguments is implemented in the *current* class (i.e. it is *not* inherited from some base class). So for example by implementing ``__eq__`` on a class yourself, ``attrs`` will deduce ``eq=False`` and will create *neither* ``__eq__`` *nor* ``__ne__`` (but Python classes come with a sensible ``__ne__`` by default, so it *should* be enough to only implement ``__eq__`` in most cases). .. warning:: If you prevent ``attrs`` from creating the ordering methods for you (``order=False``, e.g. by implementing ``__le__``), it becomes *your* responsibility to make sure its ordering is sound. The best way is to use the `functools.total_ordering` decorator. Passing ``True`` or ``False`` to *init*, *repr*, *eq*, *order*, *cmp*, or *hash* overrides whatever *auto_detect* would determine. *auto_detect* requires Python 3. Setting it ``True`` on Python 2 raises a `PythonTooOldError`. :param bool repr: Create a ``__repr__`` method with a human readable representation of ``attrs`` attributes.. :param bool str: Create a ``__str__`` method that is identical to ``__repr__``. This is usually not necessary except for `Exception`\ s. :param Optional[bool] eq: If ``True`` or ``None`` (default), add ``__eq__`` and ``__ne__`` methods that check two instances for equality. They compare the instances as if they were tuples of their ``attrs`` attributes if and only if the types of both classes are *identical*! :param Optional[bool] order: If ``True``, add ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` methods that behave like *eq* above and allow instances to be ordered. If ``None`` (default) mirror value of *eq*. :param Optional[bool] cmp: Setting *cmp* is equivalent to setting *eq* and *order* to the same value. Must not be mixed with *eq* or *order*. :param Optional[bool] hash: If ``None`` (default), the ``__hash__`` method is generated according how *eq* and *frozen* are set. 1. If *both* are True, ``attrs`` will generate a ``__hash__`` for you. 2. If *eq* is True and *frozen* is False, ``__hash__`` will be set to None, marking it unhashable (which it is). 3. If *eq* is False, ``__hash__`` will be left untouched meaning the ``__hash__`` method of the base class will be used (if base class is ``object``, this means it will fall back to id-based hashing.). Although not recommended, you can decide for yourself and force ``attrs`` to create one (e.g. if the class is immutable even though you didn't freeze it programmatically) by passing ``True`` or not. Both of these cases are rather special and should be used carefully. See our documentation on `hashing`, Python's documentation on `object.__hash__`, and the `GitHub issue that led to the default \ behavior <https://github.com/python-attrs/attrs/issues/136>`_ for more details. :param bool init: Create a ``__init__`` method that initializes the ``attrs`` attributes. Leading underscores are stripped for the argument name. If a ``__attrs_pre_init__`` method exists on the class, it will be called before the class is initialized. If a ``__attrs_post_init__`` method exists on the class, it will be called after the class is fully initialized. If ``init`` is ``False``, an ``__attrs_init__`` method will be injected instead. This allows you to define a custom ``__init__`` method that can do pre-init work such as ``super().__init__()``, and then call ``__attrs_init__()`` and ``__attrs_post_init__()``. :param bool slots: Create a `slotted class <slotted classes>` that's more memory-efficient. Slotted classes are generally superior to the default dict classes, but have some gotchas you should know about, so we encourage you to read the `glossary entry <slotted classes>`. :param bool frozen: Make instances immutable after initialization. If someone attempts to modify a frozen instance, `attr.exceptions.FrozenInstanceError` is raised. .. note:: 1. This is achieved by installing a custom ``__setattr__`` method on your class, so you can't implement your own. 2. True immutability is impossible in Python. 3. This *does* have a minor a runtime performance `impact <how-frozen>` when initializing new instances. In other words: ``__init__`` is slightly slower with ``frozen=True``. 4. If a class is frozen, you cannot modify ``self`` in ``__attrs_post_init__`` or a self-written ``__init__``. You can circumvent that limitation by using ``object.__setattr__(self, "attribute_name", value)``. 5. Subclasses of a frozen class are frozen too. :param bool weakref_slot: Make instances weak-referenceable. This has no effect unless ``slots`` is also enabled. :param bool auto_attribs: If ``True``, collect `PEP 526`_-annotated attributes (Python 3.6 and later only) from the class body. In this case, you **must** annotate every field. If ``attrs`` encounters a field that is set to an `attr.ib` but lacks a type annotation, an `attr.exceptions.UnannotatedAttributeError` is raised. Use ``field_name: typing.Any = attr.ib(...)`` if you don't want to set a type. If you assign a value to those attributes (e.g. ``x: int = 42``), that value becomes the default value like if it were passed using ``attr.ib(default=42)``. Passing an instance of `Factory` also works as expected in most cases (see warning below). Attributes annotated as `typing.ClassVar`, and attributes that are neither annotated nor set to an `attr.ib` are **ignored**. .. warning:: For features that use the attribute name to create decorators (e.g. `validators <validators>`), you still *must* assign `attr.ib` to them. Otherwise Python will either not find the name or try to use the default value to call e.g. ``validator`` on it. These errors can be quite confusing and probably the most common bug report on our bug tracker. .. _`PEP 526`: https://www.python.org/dev/peps/pep-0526/ :param bool kw_only: Make all attributes keyword-only (Python 3+) in the generated ``__init__`` (if ``init`` is ``False``, this parameter is ignored). :param bool cache_hash: Ensure that the object's hash code is computed only once and stored on the object. If this is set to ``True``, hashing must be either explicitly or implicitly enabled for this class. If the hash code is cached, avoid any reassignments of fields involved in hash code computation or mutations of the objects those fields point to after object creation. If such changes occur, the behavior of the object's hash code is undefined. :param bool auto_exc: If the class subclasses `BaseException` (which implicitly includes any subclass of any exception), the following happens to behave like a well-behaved Python exceptions class: - the values for *eq*, *order*, and *hash* are ignored and the instances compare and hash by the instance's ids (N.B. ``attrs`` will *not* remove existing implementations of ``__hash__`` or the equality methods. It just won't add own ones.), - all attributes that are either passed into ``__init__`` or have a default value are additionally available as a tuple in the ``args`` attribute, - the value of *str* is ignored leaving ``__str__`` to base classes. :param bool collect_by_mro: Setting this to `True` fixes the way ``attrs`` collects attributes from base classes. The default behavior is incorrect in certain cases of multiple inheritance. It should be on by default but is kept off for backward-compatability. See issue `#428 <https://github.com/python-attrs/attrs/issues/428>`_ for more details. :param Optional[bool] getstate_setstate: .. note:: This is usually only interesting for slotted classes and you should probably just set *auto_detect* to `True`. If `True`, ``__getstate__`` and ``__setstate__`` are generated and attached to the class. This is necessary for slotted classes to be pickleable. If left `None`, it's `True` by default for slotted classes and ``False`` for dict classes. If *auto_detect* is `True`, and *getstate_setstate* is left `None`, and **either** ``__getstate__`` or ``__setstate__`` is detected directly on the class (i.e. not inherited), it is set to `False` (this is usually what you want). :param on_setattr: A callable that is run whenever the user attempts to set an attribute (either by assignment like ``i.x = 42`` or by using `setattr` like ``setattr(i, "x", 42)``). It receives the same arguments as validators: the instance, the attribute that is being modified, and the new value. If no exception is raised, the attribute is set to the return value of the callable. If a list of callables is passed, they're automatically wrapped in an `attr.setters.pipe`. :param Optional[callable] field_transformer: A function that is called with the original class object and all fields right before ``attrs`` finalizes the class. You can use this, e.g., to automatically add converters or validators to fields based on their types. See `transform-fields` for more details. .. versionadded:: 16.0.0 *slots* .. versionadded:: 16.1.0 *frozen* .. versionadded:: 16.3.0 *str* .. versionadded:: 16.3.0 Support for ``__attrs_post_init__``. .. versionchanged:: 17.1.0 *hash* supports ``None`` as value which is also the default now. .. versionadded:: 17.3.0 *auto_attribs* .. versionchanged:: 18.1.0 If *these* is passed, no attributes are deleted from the class body. .. versionchanged:: 18.1.0 If *these* is ordered, the order is retained. .. versionadded:: 18.2.0 *weakref_slot* .. deprecated:: 18.2.0 ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` now raise a `DeprecationWarning` if the classes compared are subclasses of each other. ``__eq`` and ``__ne__`` never tried to compared subclasses to each other. .. versionchanged:: 19.2.0 ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` now do not consider subclasses comparable anymore. .. versionadded:: 18.2.0 *kw_only* .. versionadded:: 18.2.0 *cache_hash* .. versionadded:: 19.1.0 *auto_exc* .. deprecated:: 19.2.0 *cmp* Removal on or after 2021-06-01. .. versionadded:: 19.2.0 *eq* and *order* .. versionadded:: 20.1.0 *auto_detect* .. versionadded:: 20.1.0 *collect_by_mro* .. versionadded:: 20.1.0 *getstate_setstate* .. versionadded:: 20.1.0 *on_setattr* .. versionadded:: 20.3.0 *field_transformer* .. versionchanged:: 21.1.0 ``init=False`` injects ``__attrs_init__`` .. versionchanged:: 21.1.0 Support for ``__attrs_pre_init__`` .. versionchanged:: 21.1.0 *cmp* undeprecated attrs(maybe_cls=None, these=None, repr_ns=None, repr=None, cmp=None, hash=None, init=None, slots=False, frozen=False, weakref_slot=True, str=False, auto_attribs=False, kw_only=False, cache_hash=False, auto_exc=False, eq=None, order=None, auto_detect=False, collect_by_mro=False, getstate_setstate=None, on_setattr=None, field_transformer=None) A class decorator that adds `dunder <https://wiki.python.org/moin/DunderAlias>`_\ -methods according to the specified attributes using `attr.ib` or the *these* argument. :param these: A dictionary of name to `attr.ib` mappings. This is useful to avoid the definition of your attributes within the class body because you can't (e.g. if you want to add ``__repr__`` methods to Django models) or don't want to. If *these* is not ``None``, ``attrs`` will *not* search the class body for attributes and will *not* remove any attributes from it. If *these* is an ordered dict (`dict` on Python 3.6+, `collections.OrderedDict` otherwise), the order is deduced from the order of the attributes inside *these*. Otherwise the order of the definition of the attributes is used. :type these: `dict` of `str` to `attr.ib` :param str repr_ns: When using nested classes, there's no way in Python 2 to automatically detect that. Therefore it's possible to set the namespace explicitly for a more meaningful ``repr`` output. :param bool auto_detect: Instead of setting the *init*, *repr*, *eq*, *order*, and *hash* arguments explicitly, assume they are set to ``True`` **unless any** of the involved methods for one of the arguments is implemented in the *current* class (i.e. it is *not* inherited from some base class). So for example by implementing ``__eq__`` on a class yourself, ``attrs`` will deduce ``eq=False`` and will create *neither* ``__eq__`` *nor* ``__ne__`` (but Python classes come with a sensible ``__ne__`` by default, so it *should* be enough to only implement ``__eq__`` in most cases). .. warning:: If you prevent ``attrs`` from creating the ordering methods for you (``order=False``, e.g. by implementing ``__le__``), it becomes *your* responsibility to make sure its ordering is sound. The best way is to use the `functools.total_ordering` decorator. Passing ``True`` or ``False`` to *init*, *repr*, *eq*, *order*, *cmp*, or *hash* overrides whatever *auto_detect* would determine. *auto_detect* requires Python 3. Setting it ``True`` on Python 2 raises a `PythonTooOldError`. :param bool repr: Create a ``__repr__`` method with a human readable representation of ``attrs`` attributes.. :param bool str: Create a ``__str__`` method that is identical to ``__repr__``. This is usually not necessary except for `Exception`\ s. :param Optional[bool] eq: If ``True`` or ``None`` (default), add ``__eq__`` and ``__ne__`` methods that check two instances for equality. They compare the instances as if they were tuples of their ``attrs`` attributes if and only if the types of both classes are *identical*! :param Optional[bool] order: If ``True``, add ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` methods that behave like *eq* above and allow instances to be ordered. If ``None`` (default) mirror value of *eq*. :param Optional[bool] cmp: Setting *cmp* is equivalent to setting *eq* and *order* to the same value. Must not be mixed with *eq* or *order*. :param Optional[bool] hash: If ``None`` (default), the ``__hash__`` method is generated according how *eq* and *frozen* are set. 1. If *both* are True, ``attrs`` will generate a ``__hash__`` for you. 2. If *eq* is True and *frozen* is False, ``__hash__`` will be set to None, marking it unhashable (which it is). 3. If *eq* is False, ``__hash__`` will be left untouched meaning the ``__hash__`` method of the base class will be used (if base class is ``object``, this means it will fall back to id-based hashing.). Although not recommended, you can decide for yourself and force ``attrs`` to create one (e.g. if the class is immutable even though you didn't freeze it programmatically) by passing ``True`` or not. Both of these cases are rather special and should be used carefully. See our documentation on `hashing`, Python's documentation on `object.__hash__`, and the `GitHub issue that led to the default \ behavior <https://github.com/python-attrs/attrs/issues/136>`_ for more details. :param bool init: Create a ``__init__`` method that initializes the ``attrs`` attributes. Leading underscores are stripped for the argument name. If a ``__attrs_pre_init__`` method exists on the class, it will be called before the class is initialized. If a ``__attrs_post_init__`` method exists on the class, it will be called after the class is fully initialized. If ``init`` is ``False``, an ``__attrs_init__`` method will be injected instead. This allows you to define a custom ``__init__`` method that can do pre-init work such as ``super().__init__()``, and then call ``__attrs_init__()`` and ``__attrs_post_init__()``. :param bool slots: Create a `slotted class <slotted classes>` that's more memory-efficient. Slotted classes are generally superior to the default dict classes, but have some gotchas you should know about, so we encourage you to read the `glossary entry <slotted classes>`. :param bool frozen: Make instances immutable after initialization. If someone attempts to modify a frozen instance, `attr.exceptions.FrozenInstanceError` is raised. .. note:: 1. This is achieved by installing a custom ``__setattr__`` method on your class, so you can't implement your own. 2. True immutability is impossible in Python. 3. This *does* have a minor a runtime performance `impact <how-frozen>` when initializing new instances. In other words: ``__init__`` is slightly slower with ``frozen=True``. 4. If a class is frozen, you cannot modify ``self`` in ``__attrs_post_init__`` or a self-written ``__init__``. You can circumvent that limitation by using ``object.__setattr__(self, "attribute_name", value)``. 5. Subclasses of a frozen class are frozen too. :param bool weakref_slot: Make instances weak-referenceable. This has no effect unless ``slots`` is also enabled. :param bool auto_attribs: If ``True``, collect `PEP 526`_-annotated attributes (Python 3.6 and later only) from the class body. In this case, you **must** annotate every field. If ``attrs`` encounters a field that is set to an `attr.ib` but lacks a type annotation, an `attr.exceptions.UnannotatedAttributeError` is raised. Use ``field_name: typing.Any = attr.ib(...)`` if you don't want to set a type. If you assign a value to those attributes (e.g. ``x: int = 42``), that value becomes the default value like if it were passed using ``attr.ib(default=42)``. Passing an instance of `Factory` also works as expected in most cases (see warning below). Attributes annotated as `typing.ClassVar`, and attributes that are neither annotated nor set to an `attr.ib` are **ignored**. .. warning:: For features that use the attribute name to create decorators (e.g. `validators <validators>`), you still *must* assign `attr.ib` to them. Otherwise Python will either not find the name or try to use the default value to call e.g. ``validator`` on it. These errors can be quite confusing and probably the most common bug report on our bug tracker. .. _`PEP 526`: https://www.python.org/dev/peps/pep-0526/ :param bool kw_only: Make all attributes keyword-only (Python 3+) in the generated ``__init__`` (if ``init`` is ``False``, this parameter is ignored). :param bool cache_hash: Ensure that the object's hash code is computed only once and stored on the object. If this is set to ``True``, hashing must be either explicitly or implicitly enabled for this class. If the hash code is cached, avoid any reassignments of fields involved in hash code computation or mutations of the objects those fields point to after object creation. If such changes occur, the behavior of the object's hash code is undefined. :param bool auto_exc: If the class subclasses `BaseException` (which implicitly includes any subclass of any exception), the following happens to behave like a well-behaved Python exceptions class: - the values for *eq*, *order*, and *hash* are ignored and the instances compare and hash by the instance's ids (N.B. ``attrs`` will *not* remove existing implementations of ``__hash__`` or the equality methods. It just won't add own ones.), - all attributes that are either passed into ``__init__`` or have a default value are additionally available as a tuple in the ``args`` attribute, - the value of *str* is ignored leaving ``__str__`` to base classes. :param bool collect_by_mro: Setting this to `True` fixes the way ``attrs`` collects attributes from base classes. The default behavior is incorrect in certain cases of multiple inheritance. It should be on by default but is kept off for backward-compatability. See issue `#428 <https://github.com/python-attrs/attrs/issues/428>`_ for more details. :param Optional[bool] getstate_setstate: .. note:: This is usually only interesting for slotted classes and you should probably just set *auto_detect* to `True`. If `True`, ``__getstate__`` and ``__setstate__`` are generated and attached to the class. This is necessary for slotted classes to be pickleable. If left `None`, it's `True` by default for slotted classes and ``False`` for dict classes. If *auto_detect* is `True`, and *getstate_setstate* is left `None`, and **either** ``__getstate__`` or ``__setstate__`` is detected directly on the class (i.e. not inherited), it is set to `False` (this is usually what you want). :param on_setattr: A callable that is run whenever the user attempts to set an attribute (either by assignment like ``i.x = 42`` or by using `setattr` like ``setattr(i, "x", 42)``). It receives the same arguments as validators: the instance, the attribute that is being modified, and the new value. If no exception is raised, the attribute is set to the return value of the callable. If a list of callables is passed, they're automatically wrapped in an `attr.setters.pipe`. :param Optional[callable] field_transformer: A function that is called with the original class object and all fields right before ``attrs`` finalizes the class. You can use this, e.g., to automatically add converters or validators to fields based on their types. See `transform-fields` for more details. .. versionadded:: 16.0.0 *slots* .. versionadded:: 16.1.0 *frozen* .. versionadded:: 16.3.0 *str* .. versionadded:: 16.3.0 Support for ``__attrs_post_init__``. .. versionchanged:: 17.1.0 *hash* supports ``None`` as value which is also the default now. .. versionadded:: 17.3.0 *auto_attribs* .. versionchanged:: 18.1.0 If *these* is passed, no attributes are deleted from the class body. .. versionchanged:: 18.1.0 If *these* is ordered, the order is retained. .. versionadded:: 18.2.0 *weakref_slot* .. deprecated:: 18.2.0 ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` now raise a `DeprecationWarning` if the classes compared are subclasses of each other. ``__eq`` and ``__ne__`` never tried to compared subclasses to each other. .. versionchanged:: 19.2.0 ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` now do not consider subclasses comparable anymore. .. versionadded:: 18.2.0 *kw_only* .. versionadded:: 18.2.0 *cache_hash* .. versionadded:: 19.1.0 *auto_exc* .. deprecated:: 19.2.0 *cmp* Removal on or after 2021-06-01. .. versionadded:: 19.2.0 *eq* and *order* .. versionadded:: 20.1.0 *auto_detect* .. versionadded:: 20.1.0 *collect_by_mro* .. versionadded:: 20.1.0 *getstate_setstate* .. versionadded:: 20.1.0 *on_setattr* .. versionadded:: 20.3.0 *field_transformer* .. versionchanged:: 21.1.0 ``init=False`` injects ``__attrs_init__`` .. versionchanged:: 21.1.0 Support for ``__attrs_pre_init__`` .. versionchanged:: 21.1.0 *cmp* undeprecated cmp_using(eq=None, lt=None, le=None, gt=None, ge=None, require_same_type=True, class_name='Comparable') Create a class that can be passed into `attr.ib`'s ``eq``, ``order``, and ``cmp`` arguments to customize field comparison. The resulting class will have a full set of ordering methods if at least one of ``{lt, le, gt, ge}`` and ``eq`` are provided. :param Optional[callable] eq: `callable` used to evaluate equality of two objects. :param Optional[callable] lt: `callable` used to evaluate whether one object is less than another object. :param Optional[callable] le: `callable` used to evaluate whether one object is less than or equal to another object. :param Optional[callable] gt: `callable` used to evaluate whether one object is greater than another object. :param Optional[callable] ge: `callable` used to evaluate whether one object is greater than or equal to another object. :param bool require_same_type: When `True`, equality and ordering methods will return `NotImplemented` if objects are not of the same type. :param Optional[str] class_name: Name of class. Defaults to 'Comparable'. See `comparison` for more details. .. versionadded:: 21.1.0 evolve(inst, **changes) Create a new instance, based on *inst* with *changes* applied. :param inst: Instance of a class with ``attrs`` attributes. :param changes: Keyword changes in the new copy. :return: A copy of inst with *changes* incorporated. :raise TypeError: If *attr_name* couldn't be found in the class ``__init__``. :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs`` class. .. versionadded:: 17.1.0 fields(cls) Return the tuple of ``attrs`` attributes for a class. The tuple also allows accessing the fields by their names (see below for examples). :param type cls: Class to introspect. :raise TypeError: If *cls* is not a class. :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs`` class. :rtype: tuple (with name accessors) of `attr.Attribute` .. versionchanged:: 16.2.0 Returned tuple allows accessing the fields by name. fields_dict(cls) Return an ordered dictionary of ``attrs`` attributes for a class, whose keys are the attribute names. :param type cls: Class to introspect. :raise TypeError: If *cls* is not a class. :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs`` class. :rtype: an ordered dict where keys are attribute names and values are `attr.Attribute`\ s. This will be a `dict` if it's naturally ordered like on Python 3.6+ or an :class:`~collections.OrderedDict` otherwise. .. versionadded:: 18.1.0 get_run_validators() Return whether or not validators are run. has(cls) Check whether *cls* is a class with ``attrs`` attributes. :param type cls: Class to introspect. :raise TypeError: If *cls* is not a class. :rtype: bool ib = attrib(default=NOTHING, validator=None, repr=True, cmp=None, hash=None, init=True, metadata=None, type=None, converter=None, factory=None, kw_only=False, eq=None, order=None, on_setattr=None) Create a new attribute on a class. .. warning:: Does *not* do anything unless the class is also decorated with `attr.s`! :param default: A value that is used if an ``attrs``-generated ``__init__`` is used and no value is passed while instantiating or the attribute is excluded using ``init=False``. If the value is an instance of `Factory`, its callable will be used to construct a new value (useful for mutable data types like lists or dicts). If a default is not set (or set manually to `attr.NOTHING`), a value *must* be supplied when instantiating; otherwise a `TypeError` will be raised. The default can also be set using decorator notation as shown below. :type default: Any value :param callable factory: Syntactic sugar for ``default=attr.Factory(factory)``. :param validator: `callable` that is called by ``attrs``-generated ``__init__`` methods after the instance has been initialized. They receive the initialized instance, the `Attribute`, and the passed value. The return value is *not* inspected so the validator has to throw an exception itself. If a `list` is passed, its items are treated as validators and must all pass. Validators can be globally disabled and re-enabled using `get_run_validators`. The validator can also be set using decorator notation as shown below. :type validator: `callable` or a `list` of `callable`\ s. :param repr: Include this attribute in the generated ``__repr__`` method. If ``True``, include the attribute; if ``False``, omit it. By default, the built-in ``repr()`` function is used. To override how the attribute value is formatted, pass a ``callable`` that takes a single value and returns a string. Note that the resulting string is used as-is, i.e. it will be used directly *instead* of calling ``repr()`` (the default). :type repr: a `bool` or a `callable` to use a custom function. :param eq: If ``True`` (default), include this attribute in the generated ``__eq__`` and ``__ne__`` methods that check two instances for equality. To override how the attribute value is compared, pass a ``callable`` that takes a single value and returns the value to be compared. :type eq: a `bool` or a `callable`. :param order: If ``True`` (default), include this attributes in the generated ``__lt__``, ``__le__``, ``__gt__`` and ``__ge__`` methods. To override how the attribute value is ordered, pass a ``callable`` that takes a single value and returns the value to be ordered. :type order: a `bool` or a `callable`. :param cmp: Setting *cmp* is equivalent to setting *eq* and *order* to the same value. Must not be mixed with *eq* or *order*. :type cmp: a `bool` or a `callable`. :param Optional[bool] hash: Include this attribute in the generated ``__hash__`` method. If ``None`` (default), mirror *eq*'s value. This is the correct behavior according the Python spec. Setting this value to anything else than ``None`` is *discouraged*. :param bool init: Include this attribute in the generated ``__init__`` method. It is possible to set this to ``False`` and set a default value. In that case this attributed is unconditionally initialized with the specified default value or factory. :param callable converter: `callable` that is called by ``attrs``-generated ``__init__`` methods to convert attribute's value to the desired format. It is given the passed-in value, and the returned value will be used as the new value of the attribute. The value is converted before being passed to the validator, if any. :param metadata: An arbitrary mapping, to be used by third-party components. See `extending_metadata`. :param type: The type of the attribute. In Python 3.6 or greater, the preferred method to specify the type is using a variable annotation (see `PEP 526 <https://www.python.org/dev/peps/pep-0526/>`_). This argument is provided for backward compatibility. Regardless of the approach used, the type will be stored on ``Attribute.type``. Please note that ``attrs`` doesn't do anything with this metadata by itself. You can use it as part of your own code or for `static type checking <types>`. :param kw_only: Make this attribute keyword-only (Python 3+) in the generated ``__init__`` (if ``init`` is ``False``, this parameter is ignored). :param on_setattr: Allows to overwrite the *on_setattr* setting from `attr.s`. If left `None`, the *on_setattr* value from `attr.s` is used. Set to `attr.setters.NO_OP` to run **no** `setattr` hooks for this attribute -- regardless of the setting in `attr.s`. :type on_setattr: `callable`, or a list of callables, or `None`, or `attr.setters.NO_OP` .. versionadded:: 15.2.0 *convert* .. versionadded:: 16.3.0 *metadata* .. versionchanged:: 17.1.0 *validator* can be a ``list`` now. .. versionchanged:: 17.1.0 *hash* is ``None`` and therefore mirrors *eq* by default. .. versionadded:: 17.3.0 *type* .. deprecated:: 17.4.0 *convert* .. versionadded:: 17.4.0 *converter* as a replacement for the deprecated *convert* to achieve consistency with other noun-based arguments. .. versionadded:: 18.1.0 ``factory=f`` is syntactic sugar for ``default=attr.Factory(f)``. .. versionadded:: 18.2.0 *kw_only* .. versionchanged:: 19.2.0 *convert* keyword argument removed. .. versionchanged:: 19.2.0 *repr* also accepts a custom callable. .. deprecated:: 19.2.0 *cmp* Removal on or after 2021-06-01. .. versionadded:: 19.2.0 *eq* and *order* .. versionadded:: 20.1.0 *on_setattr* .. versionchanged:: 20.3.0 *kw_only* backported to Python 2 .. versionchanged:: 21.1.0 *eq*, *order*, and *cmp* also accept a custom callable .. versionchanged:: 21.1.0 *cmp* undeprecated make_class(name, attrs, bases=(<class 'object'>,), **attributes_arguments) A quick way to create a new class called *name* with *attrs*. :param str name: The name for the new class. :param attrs: A list of names or a dictionary of mappings of names to attributes. If *attrs* is a list or an ordered dict (`dict` on Python 3.6+, `collections.OrderedDict` otherwise), the order is deduced from the order of the names or attributes inside *attrs*. Otherwise the order of the definition of the attributes is used. :type attrs: `list` or `dict` :param tuple bases: Classes that the new class will subclass. :param attributes_arguments: Passed unmodified to `attr.s`. :return: A new class with *attrs*. :rtype: type .. versionadded:: 17.1.0 *bases* .. versionchanged:: 18.1.0 If *attrs* is ordered, the order is retained. resolve_types(cls, globalns=None, localns=None, attribs=None) Resolve any strings and forward annotations in type annotations. This is only required if you need concrete types in `Attribute`'s *type* field. In other words, you don't need to resolve your types if you only use them for static type checking. With no arguments, names will be looked up in the module in which the class was created. If this is not what you want, e.g. if the name only exists inside a method, you may pass *globalns* or *localns* to specify other dictionaries in which to look up these names. See the docs of `typing.get_type_hints` for more details. :param type cls: Class to resolve. :param Optional[dict] globalns: Dictionary containing global variables. :param Optional[dict] localns: Dictionary containing local variables. :param Optional[list] attribs: List of attribs for the given class. This is necessary when calling from inside a ``field_transformer`` since *cls* is not an ``attrs`` class yet. :raise TypeError: If *cls* is not a class. :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs`` class and you didn't pass any attribs. :raise NameError: If types cannot be resolved because of missing variables. :returns: *cls* so you can use this function also as a class decorator. Please note that you have to apply it **after** `attr.s`. That means the decorator has to come in the line **before** `attr.s`. .. versionadded:: 20.1.0 .. versionadded:: 21.1.0 *attribs* s = attrs(maybe_cls=None, these=None, repr_ns=None, repr=None, cmp=None, hash=None, init=None, slots=False, frozen=False, weakref_slot=True, str=False, auto_attribs=False, kw_only=False, cache_hash=False, auto_exc=False, eq=None, order=None, auto_detect=False, collect_by_mro=False, getstate_setstate=None, on_setattr=None, field_transformer=None) A class decorator that adds `dunder <https://wiki.python.org/moin/DunderAlias>`_\ -methods according to the specified attributes using `attr.ib` or the *these* argument. :param these: A dictionary of name to `attr.ib` mappings. This is useful to avoid the definition of your attributes within the class body because you can't (e.g. if you want to add ``__repr__`` methods to Django models) or don't want to. If *these* is not ``None``, ``attrs`` will *not* search the class body for attributes and will *not* remove any attributes from it. If *these* is an ordered dict (`dict` on Python 3.6+, `collections.OrderedDict` otherwise), the order is deduced from the order of the attributes inside *these*. Otherwise the order of the definition of the attributes is used. :type these: `dict` of `str` to `attr.ib` :param str repr_ns: When using nested classes, there's no way in Python 2 to automatically detect that. Therefore it's possible to set the namespace explicitly for a more meaningful ``repr`` output. :param bool auto_detect: Instead of setting the *init*, *repr*, *eq*, *order*, and *hash* arguments explicitly, assume they are set to ``True`` **unless any** of the involved methods for one of the arguments is implemented in the *current* class (i.e. it is *not* inherited from some base class). So for example by implementing ``__eq__`` on a class yourself, ``attrs`` will deduce ``eq=False`` and will create *neither* ``__eq__`` *nor* ``__ne__`` (but Python classes come with a sensible ``__ne__`` by default, so it *should* be enough to only implement ``__eq__`` in most cases). .. warning:: If you prevent ``attrs`` from creating the ordering methods for you (``order=False``, e.g. by implementing ``__le__``), it becomes *your* responsibility to make sure its ordering is sound. The best way is to use the `functools.total_ordering` decorator. Passing ``True`` or ``False`` to *init*, *repr*, *eq*, *order*, *cmp*, or *hash* overrides whatever *auto_detect* would determine. *auto_detect* requires Python 3. Setting it ``True`` on Python 2 raises a `PythonTooOldError`. :param bool repr: Create a ``__repr__`` method with a human readable representation of ``attrs`` attributes.. :param bool str: Create a ``__str__`` method that is identical to ``__repr__``. This is usually not necessary except for `Exception`\ s. :param Optional[bool] eq: If ``True`` or ``None`` (default), add ``__eq__`` and ``__ne__`` methods that check two instances for equality. They compare the instances as if they were tuples of their ``attrs`` attributes if and only if the types of both classes are *identical*! :param Optional[bool] order: If ``True``, add ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` methods that behave like *eq* above and allow instances to be ordered. If ``None`` (default) mirror value of *eq*. :param Optional[bool] cmp: Setting *cmp* is equivalent to setting *eq* and *order* to the same value. Must not be mixed with *eq* or *order*. :param Optional[bool] hash: If ``None`` (default), the ``__hash__`` method is generated according how *eq* and *frozen* are set. 1. If *both* are True, ``attrs`` will generate a ``__hash__`` for you. 2. If *eq* is True and *frozen* is False, ``__hash__`` will be set to None, marking it unhashable (which it is). 3. If *eq* is False, ``__hash__`` will be left untouched meaning the ``__hash__`` method of the base class will be used (if base class is ``object``, this means it will fall back to id-based hashing.). Although not recommended, you can decide for yourself and force ``attrs`` to create one (e.g. if the class is immutable even though you didn't freeze it programmatically) by passing ``True`` or not. Both of these cases are rather special and should be used carefully. See our documentation on `hashing`, Python's documentation on `object.__hash__`, and the `GitHub issue that led to the default \ behavior <https://github.com/python-attrs/attrs/issues/136>`_ for more details. :param bool init: Create a ``__init__`` method that initializes the ``attrs`` attributes. Leading underscores are stripped for the argument name. If a ``__attrs_pre_init__`` method exists on the class, it will be called before the class is initialized. If a ``__attrs_post_init__`` method exists on the class, it will be called after the class is fully initialized. If ``init`` is ``False``, an ``__attrs_init__`` method will be injected instead. This allows you to define a custom ``__init__`` method that can do pre-init work such as ``super().__init__()``, and then call ``__attrs_init__()`` and ``__attrs_post_init__()``. :param bool slots: Create a `slotted class <slotted classes>` that's more memory-efficient. Slotted classes are generally superior to the default dict classes, but have some gotchas you should know about, so we encourage you to read the `glossary entry <slotted classes>`. :param bool frozen: Make instances immutable after initialization. If someone attempts to modify a frozen instance, `attr.exceptions.FrozenInstanceError` is raised. .. note:: 1. This is achieved by installing a custom ``__setattr__`` method on your class, so you can't implement your own. 2. True immutability is impossible in Python. 3. This *does* have a minor a runtime performance `impact <how-frozen>` when initializing new instances. In other words: ``__init__`` is slightly slower with ``frozen=True``. 4. If a class is frozen, you cannot modify ``self`` in ``__attrs_post_init__`` or a self-written ``__init__``. You can circumvent that limitation by using ``object.__setattr__(self, "attribute_name", value)``. 5. Subclasses of a frozen class are frozen too. :param bool weakref_slot: Make instances weak-referenceable. This has no effect unless ``slots`` is also enabled. :param bool auto_attribs: If ``True``, collect `PEP 526`_-annotated attributes (Python 3.6 and later only) from the class body. In this case, you **must** annotate every field. If ``attrs`` encounters a field that is set to an `attr.ib` but lacks a type annotation, an `attr.exceptions.UnannotatedAttributeError` is raised. Use ``field_name: typing.Any = attr.ib(...)`` if you don't want to set a type. If you assign a value to those attributes (e.g. ``x: int = 42``), that value becomes the default value like if it were passed using ``attr.ib(default=42)``. Passing an instance of `Factory` also works as expected in most cases (see warning below). Attributes annotated as `typing.ClassVar`, and attributes that are neither annotated nor set to an `attr.ib` are **ignored**. .. warning:: For features that use the attribute name to create decorators (e.g. `validators <validators>`), you still *must* assign `attr.ib` to them. Otherwise Python will either not find the name or try to use the default value to call e.g. ``validator`` on it. These errors can be quite confusing and probably the most common bug report on our bug tracker. .. _`PEP 526`: https://www.python.org/dev/peps/pep-0526/ :param bool kw_only: Make all attributes keyword-only (Python 3+) in the generated ``__init__`` (if ``init`` is ``False``, this parameter is ignored). :param bool cache_hash: Ensure that the object's hash code is computed only once and stored on the object. If this is set to ``True``, hashing must be either explicitly or implicitly enabled for this class. If the hash code is cached, avoid any reassignments of fields involved in hash code computation or mutations of the objects those fields point to after object creation. If such changes occur, the behavior of the object's hash code is undefined. :param bool auto_exc: If the class subclasses `BaseException` (which implicitly includes any subclass of any exception), the following happens to behave like a well-behaved Python exceptions class: - the values for *eq*, *order*, and *hash* are ignored and the instances compare and hash by the instance's ids (N.B. ``attrs`` will *not* remove existing implementations of ``__hash__`` or the equality methods. It just won't add own ones.), - all attributes that are either passed into ``__init__`` or have a default value are additionally available as a tuple in the ``args`` attribute, - the value of *str* is ignored leaving ``__str__`` to base classes. :param bool collect_by_mro: Setting this to `True` fixes the way ``attrs`` collects attributes from base classes. The default behavior is incorrect in certain cases of multiple inheritance. It should be on by default but is kept off for backward-compatability. See issue `#428 <https://github.com/python-attrs/attrs/issues/428>`_ for more details. :param Optional[bool] getstate_setstate: .. note:: This is usually only interesting for slotted classes and you should probably just set *auto_detect* to `True`. If `True`, ``__getstate__`` and ``__setstate__`` are generated and attached to the class. This is necessary for slotted classes to be pickleable. If left `None`, it's `True` by default for slotted classes and ``False`` for dict classes. If *auto_detect* is `True`, and *getstate_setstate* is left `None`, and **either** ``__getstate__`` or ``__setstate__`` is detected directly on the class (i.e. not inherited), it is set to `False` (this is usually what you want). :param on_setattr: A callable that is run whenever the user attempts to set an attribute (either by assignment like ``i.x = 42`` or by using `setattr` like ``setattr(i, "x", 42)``). It receives the same arguments as validators: the instance, the attribute that is being modified, and the new value. If no exception is raised, the attribute is set to the return value of the callable. If a list of callables is passed, they're automatically wrapped in an `attr.setters.pipe`. :param Optional[callable] field_transformer: A function that is called with the original class object and all fields right before ``attrs`` finalizes the class. You can use this, e.g., to automatically add converters or validators to fields based on their types. See `transform-fields` for more details. .. versionadded:: 16.0.0 *slots* .. versionadded:: 16.1.0 *frozen* .. versionadded:: 16.3.0 *str* .. versionadded:: 16.3.0 Support for ``__attrs_post_init__``. .. versionchanged:: 17.1.0 *hash* supports ``None`` as value which is also the default now. .. versionadded:: 17.3.0 *auto_attribs* .. versionchanged:: 18.1.0 If *these* is passed, no attributes are deleted from the class body. .. versionchanged:: 18.1.0 If *these* is ordered, the order is retained. .. versionadded:: 18.2.0 *weakref_slot* .. deprecated:: 18.2.0 ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` now raise a `DeprecationWarning` if the classes compared are subclasses of each other. ``__eq`` and ``__ne__`` never tried to compared subclasses to each other. .. versionchanged:: 19.2.0 ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` now do not consider subclasses comparable anymore. .. versionadded:: 18.2.0 *kw_only* .. versionadded:: 18.2.0 *cache_hash* .. versionadded:: 19.1.0 *auto_exc* .. deprecated:: 19.2.0 *cmp* Removal on or after 2021-06-01. .. versionadded:: 19.2.0 *eq* and *order* .. versionadded:: 20.1.0 *auto_detect* .. versionadded:: 20.1.0 *collect_by_mro* .. versionadded:: 20.1.0 *getstate_setstate* .. versionadded:: 20.1.0 *on_setattr* .. versionadded:: 20.3.0 *field_transformer* .. versionchanged:: 21.1.0 ``init=False`` injects ``__attrs_init__`` .. versionchanged:: 21.1.0 Support for ``__attrs_pre_init__`` .. versionchanged:: 21.1.0 *cmp* undeprecated set_run_validators(run) Set whether or not validators are run. By default, they are run. validate(inst) Validate all attributes on *inst* that have a validator. Leaves all exceptions through. :param inst: Instance of a class with ``attrs`` attributes. DATA NOTHING = NOTHING __all__ = ['Attribute', 'Factory', 'NOTHING', 'asdict', 'assoc', 'astu... __copyright__ = 'Copyright (c) 2015 Hynek Schlawack' __description__ = 'Classes Without Boilerplate' __email__ = 'hs AT ox.cx' __license__ = 'MIT' __title__ = 'attrs' __uri__ = 'https://www.attrs.org/' __url__ = 'https://www.attrs.org/' __version_info__ = VersionInfo(year=21, minor=2, micro=0, releaselevel... VERSION 21.2.0 AUTHOR Hynek Schlawack FILE /usr/lib/python3/dist-packages/attr/__init__.py
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