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docs: fix over-linking in dataclasses.rst (#117005)

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@ -1,5 +1,5 @@
:mod:`dataclasses` --- Data Classes :mod:`!dataclasses` --- Data Classes
=================================== ====================================
.. module:: dataclasses .. module:: dataclasses
:synopsis: Generate special methods on user-defined classes. :synopsis: Generate special methods on user-defined classes.
@ -31,7 +31,7 @@ using :pep:`526` type annotations. For example, this code::
def total_cost(self) -> float: def total_cost(self) -> float:
return self.unit_price * self.quantity_on_hand return self.unit_price * self.quantity_on_hand
will add, among other things, a :meth:`~object.__init__` that looks like:: will add, among other things, a :meth:`!__init__` that looks like::
def __init__(self, name: str, unit_price: float, quantity_on_hand: int = 0): def __init__(self, name: str, unit_price: float, quantity_on_hand: int = 0):
self.name = name self.name = name
@ -49,26 +49,26 @@ Module contents
.. decorator:: dataclass(*, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False, slots=False, weakref_slot=False) .. decorator:: dataclass(*, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False, slots=False, weakref_slot=False)
This function is a :term:`decorator` that is used to add generated This function is a :term:`decorator` that is used to add generated
:term:`special method`\s to classes, as described below. :term:`special methods <special method>` to classes, as described below.
The :func:`dataclass` decorator examines the class to find The ``@dataclass`` decorator examines the class to find
``field``\s. A ``field`` is defined as a class variable that has a ``field``\s. A ``field`` is defined as a class variable that has a
:term:`type annotation <variable annotation>`. With two :term:`type annotation <variable annotation>`. With two
exceptions described below, nothing in :func:`dataclass` exceptions described below, nothing in ``@dataclass``
examines the type specified in the variable annotation. examines the type specified in the variable annotation.
The order of the fields in all of the generated methods is the The order of the fields in all of the generated methods is the
order in which they appear in the class definition. order in which they appear in the class definition.
The :func:`dataclass` decorator will add various "dunder" methods to The ``@dataclass`` decorator will add various "dunder" methods to
the class, described below. If any of the added methods already the class, described below. If any of the added methods already
exist in the class, the behavior depends on the parameter, as documented exist in the class, the behavior depends on the parameter, as documented
below. The decorator returns the same class that it is called on; no new below. The decorator returns the same class that it is called on; no new
class is created. class is created.
If :func:`dataclass` is used just as a simple decorator with no parameters, If ``@dataclass`` is used just as a simple decorator with no parameters,
it acts as if it has the default values documented in this it acts as if it has the default values documented in this
signature. That is, these three uses of :func:`dataclass` are signature. That is, these three uses of ``@dataclass`` are
equivalent:: equivalent::
@dataclass @dataclass
@ -84,12 +84,12 @@ Module contents
class C: class C:
... ...
The parameters to :func:`dataclass` are: The parameters to ``@dataclass`` are:
- ``init``: If true (the default), a :meth:`~object.__init__` method will be - ``init``: If true (the default), a :meth:`~object.__init__` method will be
generated. generated.
If the class already defines :meth:`~object.__init__`, this parameter is If the class already defines :meth:`!__init__`, this parameter is
ignored. ignored.
- ``repr``: If true (the default), a :meth:`~object.__repr__` method will be - ``repr``: If true (the default), a :meth:`~object.__repr__` method will be
@ -99,7 +99,7 @@ Module contents
are not included. For example: are not included. For example:
``InventoryItem(name='widget', unit_price=3.0, quantity_on_hand=10)``. ``InventoryItem(name='widget', unit_price=3.0, quantity_on_hand=10)``.
If the class already defines :meth:`~object.__repr__`, this parameter is If the class already defines :meth:`!__repr__`, this parameter is
ignored. ignored.
- ``eq``: If true (the default), an :meth:`~object.__eq__` method will be - ``eq``: If true (the default), an :meth:`~object.__eq__` method will be
@ -107,7 +107,7 @@ Module contents
of its fields, in order. Both instances in the comparison must of its fields, in order. Both instances in the comparison must
be of the identical type. be of the identical type.
If the class already defines :meth:`~object.__eq__`, this parameter is If the class already defines :meth:`!__eq__`, this parameter is
ignored. ignored.
- ``order``: If true (the default is ``False``), :meth:`~object.__lt__`, - ``order``: If true (the default is ``False``), :meth:`~object.__lt__`,
@ -117,43 +117,43 @@ Module contents
identical type. If ``order`` is true and ``eq`` is false, a identical type. If ``order`` is true and ``eq`` is false, a
:exc:`ValueError` is raised. :exc:`ValueError` is raised.
If the class already defines any of :meth:`~object.__lt__`, If the class already defines any of :meth:`!__lt__`,
:meth:`~object.__le__`, :meth:`~object.__gt__`, or :meth:`~object.__ge__`, then :meth:`!__le__`, :meth:`!__gt__`, or :meth:`!__ge__`, then
:exc:`TypeError` is raised. :exc:`TypeError` is raised.
- ``unsafe_hash``: If ``False`` (the default), a :meth:`~object.__hash__` method - ``unsafe_hash``: If ``False`` (the default), a :meth:`~object.__hash__` method
is generated according to how ``eq`` and ``frozen`` are set. is generated according to how ``eq`` and ``frozen`` are set.
:meth:`~object.__hash__` is used by built-in :meth:`hash()`, and when objects are :meth:`!__hash__` is used by built-in :meth:`hash()`, and when objects are
added to hashed collections such as dictionaries and sets. Having a added to hashed collections such as dictionaries and sets. Having a
:meth:`~object.__hash__` implies that instances of the class are immutable. :meth:`!__hash__` implies that instances of the class are immutable.
Mutability is a complicated property that depends on the programmer's Mutability is a complicated property that depends on the programmer's
intent, the existence and behavior of :meth:`~object.__eq__`, and the values of intent, the existence and behavior of :meth:`!__eq__`, and the values of
the ``eq`` and ``frozen`` flags in the :func:`dataclass` decorator. the ``eq`` and ``frozen`` flags in the ``@dataclass`` decorator.
By default, :func:`dataclass` will not implicitly add a :meth:`~object.__hash__` By default, ``@dataclass`` will not implicitly add a :meth:`~object.__hash__`
method unless it is safe to do so. Neither will it add or change an method unless it is safe to do so. Neither will it add or change an
existing explicitly defined :meth:`~object.__hash__` method. Setting the class existing explicitly defined :meth:`!__hash__` method. Setting the class
attribute ``__hash__ = None`` has a specific meaning to Python, as attribute ``__hash__ = None`` has a specific meaning to Python, as
described in the :meth:`~object.__hash__` documentation. described in the :meth:`!__hash__` documentation.
If :meth:`~object.__hash__` is not explicitly defined, or if it is set to ``None``, If :meth:`!__hash__` is not explicitly defined, or if it is set to ``None``,
then :func:`dataclass` *may* add an implicit :meth:`~object.__hash__` method. then ``@dataclass`` *may* add an implicit :meth:`!__hash__` method.
Although not recommended, you can force :func:`dataclass` to create a Although not recommended, you can force ``@dataclass`` to create a
:meth:`~object.__hash__` method with ``unsafe_hash=True``. This might be the case :meth:`!__hash__` method with ``unsafe_hash=True``. This might be the case
if your class is logically immutable but can still be mutated. if your class is logically immutable but can still be mutated.
This is a specialized use case and should be considered carefully. This is a specialized use case and should be considered carefully.
Here are the rules governing implicit creation of a :meth:`~object.__hash__` Here are the rules governing implicit creation of a :meth:`!__hash__`
method. Note that you cannot both have an explicit :meth:`~object.__hash__` method. Note that you cannot both have an explicit :meth:`!__hash__`
method in your dataclass and set ``unsafe_hash=True``; this will result method in your dataclass and set ``unsafe_hash=True``; this will result
in a :exc:`TypeError`. in a :exc:`TypeError`.
If ``eq`` and ``frozen`` are both true, by default :func:`dataclass` will If ``eq`` and ``frozen`` are both true, by default ``@dataclass`` will
generate a :meth:`~object.__hash__` method for you. If ``eq`` is true and generate a :meth:`!__hash__` method for you. If ``eq`` is true and
``frozen`` is false, :meth:`~object.__hash__` will be set to ``None``, marking it ``frozen`` is false, :meth:`!__hash__` will be set to ``None``, marking it
unhashable (which it is, since it is mutable). If ``eq`` is false, unhashable (which it is, since it is mutable). If ``eq`` is false,
:meth:`~object.__hash__` will be left untouched meaning the :meth:`~object.__hash__` :meth:`!__hash__` will be left untouched meaning the :meth:`!__hash__`
method of the superclass will be used (if the superclass is method of the superclass will be used (if the superclass is
:class:`object`, this means it will fall back to id-based hashing). :class:`object`, this means it will fall back to id-based hashing).
@ -165,7 +165,7 @@ Module contents
- ``match_args``: If true (the default is ``True``), the - ``match_args``: If true (the default is ``True``), the
``__match_args__`` tuple will be created from the list of ``__match_args__`` tuple will be created from the list of
parameters to the generated :meth:`~object.__init__` method (even if parameters to the generated :meth:`~object.__init__` method (even if
:meth:`~object.__init__` is not generated, see above). If false, or if :meth:`!__init__` is not generated, see above). If false, or if
``__match_args__`` is already defined in the class, then ``__match_args__`` is already defined in the class, then
``__match_args__`` will not be generated. ``__match_args__`` will not be generated.
@ -175,7 +175,7 @@ Module contents
fields will be marked as keyword-only. If a field is marked as fields will be marked as keyword-only. If a field is marked as
keyword-only, then the only effect is that the :meth:`~object.__init__` keyword-only, then the only effect is that the :meth:`~object.__init__`
parameter generated from a keyword-only field must be specified parameter generated from a keyword-only field must be specified
with a keyword when :meth:`~object.__init__` is called. There is no with a keyword when :meth:`!__init__` is called. There is no
effect on any other aspect of dataclasses. See the effect on any other aspect of dataclasses. See the
:term:`parameter` glossary entry for details. Also see the :term:`parameter` glossary entry for details. Also see the
:const:`KW_ONLY` section. :const:`KW_ONLY` section.
@ -184,7 +184,7 @@ Module contents
- ``slots``: If true (the default is ``False``), :attr:`~object.__slots__` attribute - ``slots``: If true (the default is ``False``), :attr:`~object.__slots__` attribute
will be generated and new class will be returned instead of the original one. will be generated and new class will be returned instead of the original one.
If :attr:`~object.__slots__` is already defined in the class, then :exc:`TypeError` If :attr:`!__slots__` is already defined in the class, then :exc:`TypeError`
is raised. is raised.
.. versionadded:: 3.10 .. versionadded:: 3.10
@ -229,7 +229,7 @@ Module contents
required. There are, however, some dataclass features that required. There are, however, some dataclass features that
require additional per-field information. To satisfy this need for require additional per-field information. To satisfy this need for
additional information, you can replace the default field value additional information, you can replace the default field value
with a call to the provided :func:`field` function. For example:: with a call to the provided :func:`!field` function. For example::
@dataclass @dataclass
class C: class C:
@ -243,10 +243,10 @@ Module contents
used because ``None`` is a valid value for some parameters with used because ``None`` is a valid value for some parameters with
a distinct meaning. No code should directly use the :const:`MISSING` value. a distinct meaning. No code should directly use the :const:`MISSING` value.
The parameters to :func:`field` are: The parameters to :func:`!field` are:
- ``default``: If provided, this will be the default value for this - ``default``: If provided, this will be the default value for this
field. This is needed because the :meth:`field` call itself field. This is needed because the :func:`!field` call itself
replaces the normal position of the default value. replaces the normal position of the default value.
- ``default_factory``: If provided, it must be a zero-argument - ``default_factory``: If provided, it must be a zero-argument
@ -293,10 +293,10 @@ Module contents
.. versionadded:: 3.10 .. versionadded:: 3.10
If the default value of a field is specified by a call to If the default value of a field is specified by a call to
:func:`field()`, then the class attribute for this field will be :func:`!field`, then the class attribute for this field will be
replaced by the specified ``default`` value. If no ``default`` is replaced by the specified ``default`` value. If no ``default`` is
provided, then the class attribute will be deleted. The intent is provided, then the class attribute will be deleted. The intent is
that after the :func:`dataclass` decorator runs, the class that after the :func:`@dataclass <dataclass>` decorator runs, the class
attributes will all contain the default values for the fields, just attributes will all contain the default values for the fields, just
as if the default value itself were specified. For example, as if the default value itself were specified. For example,
after:: after::
@ -314,10 +314,10 @@ Module contents
.. class:: Field .. class:: Field
:class:`Field` objects describe each defined field. These objects :class:`!Field` objects describe each defined field. These objects
are created internally, and are returned by the :func:`fields` are created internally, and are returned by the :func:`fields`
module-level method (see below). Users should never instantiate a module-level method (see below). Users should never instantiate a
:class:`Field` object directly. Its documented attributes are: :class:`!Field` object directly. Its documented attributes are:
- ``name``: The name of the field. - ``name``: The name of the field.
- ``type``: The type of the field. - ``type``: The type of the field.
@ -343,7 +343,7 @@ Module contents
lists, and tuples are recursed into. Other objects are copied with lists, and tuples are recursed into. Other objects are copied with
:func:`copy.deepcopy`. :func:`copy.deepcopy`.
Example of using :func:`asdict` on nested dataclasses:: Example of using :func:`!asdict` on nested dataclasses::
@dataclass @dataclass
class Point: class Point:
@ -364,7 +364,7 @@ Module contents
dict((field.name, getattr(obj, field.name)) for field in fields(obj)) dict((field.name, getattr(obj, field.name)) for field in fields(obj))
:func:`asdict` raises :exc:`TypeError` if ``obj`` is not a dataclass :func:`!asdict` raises :exc:`TypeError` if ``obj`` is not a dataclass
instance. instance.
.. function:: astuple(obj, *, tuple_factory=tuple) .. function:: astuple(obj, *, tuple_factory=tuple)
@ -384,7 +384,7 @@ Module contents
tuple(getattr(obj, field.name) for field in dataclasses.fields(obj)) tuple(getattr(obj, field.name) for field in dataclasses.fields(obj))
:func:`astuple` raises :exc:`TypeError` if ``obj`` is not a dataclass :func:`!astuple` raises :exc:`TypeError` if ``obj`` is not a dataclass
instance. instance.
.. function:: make_dataclass(cls_name, fields, *, bases=(), namespace=None, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False, slots=False, weakref_slot=False, module=None) .. function:: make_dataclass(cls_name, fields, *, bases=(), namespace=None, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False, slots=False, weakref_slot=False, module=None)
@ -397,7 +397,7 @@ Module contents
``typing.Any`` is used for ``type``. The values of ``init``, ``typing.Any`` is used for ``type``. The values of ``init``,
``repr``, ``eq``, ``order``, ``unsafe_hash``, ``frozen``, ``repr``, ``eq``, ``order``, ``unsafe_hash``, ``frozen``,
``match_args``, ``kw_only``, ``slots``, and ``weakref_slot`` have ``match_args``, ``kw_only``, ``slots``, and ``weakref_slot`` have
the same meaning as they do in :func:`dataclass`. the same meaning as they do in :func:`@dataclass <dataclass>`.
If ``module`` is defined, the ``__module__`` attribute If ``module`` is defined, the ``__module__`` attribute
of the dataclass is set to that value. of the dataclass is set to that value.
@ -405,7 +405,7 @@ Module contents
This function is not strictly required, because any Python This function is not strictly required, because any Python
mechanism for creating a new class with ``__annotations__`` can mechanism for creating a new class with ``__annotations__`` can
then apply the :func:`dataclass` function to convert that class to then apply the ``@dataclass`` function to convert that class to
a dataclass. This function is provided as a convenience. For a dataclass. This function is provided as a convenience. For
example:: example::
@ -438,15 +438,15 @@ Module contents
:meth:`__post_init__`, if present, is also called. :meth:`__post_init__`, if present, is also called.
Init-only variables without default values, if any exist, must be Init-only variables without default values, if any exist, must be
specified on the call to :func:`replace` so that they can be passed to specified on the call to :func:`!replace` so that they can be passed to
:meth:`~object.__init__` and :meth:`__post_init__`. :meth:`!__init__` and :meth:`__post_init__`.
It is an error for ``changes`` to contain any fields that are It is an error for ``changes`` to contain any fields that are
defined as having ``init=False``. A :exc:`ValueError` will be raised defined as having ``init=False``. A :exc:`ValueError` will be raised
in this case. in this case.
Be forewarned about how ``init=False`` fields work during a call to Be forewarned about how ``init=False`` fields work during a call to
:func:`replace`. They are not copied from the source object, but :func:`!replace`. They are not copied from the source object, but
rather are initialized in :meth:`__post_init__`, if they're rather are initialized in :meth:`__post_init__`, if they're
initialized at all. It is expected that ``init=False`` fields will initialized at all. It is expected that ``init=False`` fields will
be rarely and judiciously used. If they are used, it might be wise be rarely and judiciously used. If they are used, it might be wise
@ -475,11 +475,11 @@ Module contents
.. data:: KW_ONLY .. data:: KW_ONLY
A sentinel value used as a type annotation. Any fields after a A sentinel value used as a type annotation. Any fields after a
pseudo-field with the type of :const:`KW_ONLY` are marked as pseudo-field with the type of :const:`!KW_ONLY` are marked as
keyword-only fields. Note that a pseudo-field of type keyword-only fields. Note that a pseudo-field of type
:const:`KW_ONLY` is otherwise completely ignored. This includes the :const:`!KW_ONLY` is otherwise completely ignored. This includes the
name of such a field. By convention, a name of ``_`` is used for a name of such a field. By convention, a name of ``_`` is used for a
:const:`KW_ONLY` field. Keyword-only fields signify :const:`!KW_ONLY` field. Keyword-only fields signify
:meth:`~object.__init__` parameters that must be specified as keywords when :meth:`~object.__init__` parameters that must be specified as keywords when
the class is instantiated. the class is instantiated.
@ -495,7 +495,7 @@ Module contents
p = Point(0, y=1.5, z=2.0) p = Point(0, y=1.5, z=2.0)
In a single dataclass, it is an error to specify more than one In a single dataclass, it is an error to specify more than one
field whose type is :const:`KW_ONLY`. field whose type is :const:`!KW_ONLY`.
.. versionadded:: 3.10 .. versionadded:: 3.10
@ -515,9 +515,9 @@ Post-init processing
When defined on the class, it will be called by the generated When defined on the class, it will be called by the generated
:meth:`~object.__init__`, normally as ``self.__post_init__()``. :meth:`~object.__init__`, normally as ``self.__post_init__()``.
However, if any ``InitVar`` fields are defined, they will also be However, if any ``InitVar`` fields are defined, they will also be
passed to :meth:`__post_init__` in the order they were defined in the passed to :meth:`!__post_init__` in the order they were defined in the
class. If no :meth:`~object.__init__` method is generated, then class. If no :meth:`!__init__` method is generated, then
:meth:`__post_init__` will not automatically be called. :meth:`!__post_init__` will not automatically be called.
Among other uses, this allows for initializing field values that Among other uses, this allows for initializing field values that
depend on one or more other fields. For example:: depend on one or more other fields. For example::
@ -531,8 +531,8 @@ Post-init processing
def __post_init__(self): def __post_init__(self):
self.c = self.a + self.b self.c = self.a + self.b
The :meth:`~object.__init__` method generated by :func:`dataclass` does not call base The :meth:`~object.__init__` method generated by :func:`@dataclass <dataclass>` does not call base
class :meth:`~object.__init__` methods. If the base class has an :meth:`~object.__init__` method class :meth:`!__init__` methods. If the base class has an :meth:`!__init__` method
that has to be called, it is common to call this method in a that has to be called, it is common to call this method in a
:meth:`__post_init__` method:: :meth:`__post_init__` method::
@ -548,18 +548,18 @@ that has to be called, it is common to call this method in a
def __post_init__(self): def __post_init__(self):
super().__init__(self.side, self.side) super().__init__(self.side, self.side)
Note, however, that in general the dataclass-generated :meth:`~object.__init__` methods Note, however, that in general the dataclass-generated :meth:`!__init__` methods
don't need to be called, since the derived dataclass will take care of don't need to be called, since the derived dataclass will take care of
initializing all fields of any base class that is a dataclass itself. initializing all fields of any base class that is a dataclass itself.
See the section below on init-only variables for ways to pass See the section below on init-only variables for ways to pass
parameters to :meth:`__post_init__`. Also see the warning about how parameters to :meth:`!__post_init__`. Also see the warning about how
:func:`replace` handles ``init=False`` fields. :func:`replace` handles ``init=False`` fields.
Class variables Class variables
--------------- ---------------
One of the few places where :func:`dataclass` actually inspects the type One of the few places where :func:`@dataclass <dataclass>` actually inspects the type
of a field is to determine if a field is a class variable as defined of a field is to determine if a field is a class variable as defined
in :pep:`526`. It does this by checking if the type of the field is in :pep:`526`. It does this by checking if the type of the field is
``typing.ClassVar``. If a field is a ``ClassVar``, it is excluded ``typing.ClassVar``. If a field is a ``ClassVar``, it is excluded
@ -570,7 +570,7 @@ module-level :func:`fields` function.
Init-only variables Init-only variables
------------------- -------------------
Another place where :func:`dataclass` inspects a type annotation is to Another place where :func:`@dataclass <dataclass>` inspects a type annotation is to
determine if a field is an init-only variable. It does this by seeing determine if a field is an init-only variable. It does this by seeing
if the type of a field is of type ``dataclasses.InitVar``. If a field if the type of a field is of type ``dataclasses.InitVar``. If a field
is an ``InitVar``, it is considered a pseudo-field called an init-only is an ``InitVar``, it is considered a pseudo-field called an init-only
@ -602,19 +602,19 @@ Frozen instances
---------------- ----------------
It is not possible to create truly immutable Python objects. However, It is not possible to create truly immutable Python objects. However,
by passing ``frozen=True`` to the :meth:`dataclass` decorator you can by passing ``frozen=True`` to the :func:`@dataclass <dataclass>` decorator you can
emulate immutability. In that case, dataclasses will add emulate immutability. In that case, dataclasses will add
:meth:`~object.__setattr__` and :meth:`~object.__delattr__` methods to the class. These :meth:`~object.__setattr__` and :meth:`~object.__delattr__` methods to the class. These
methods will raise a :exc:`FrozenInstanceError` when invoked. methods will raise a :exc:`FrozenInstanceError` when invoked.
There is a tiny performance penalty when using ``frozen=True``: There is a tiny performance penalty when using ``frozen=True``:
:meth:`~object.__init__` cannot use simple assignment to initialize fields, and :meth:`~object.__init__` cannot use simple assignment to initialize fields, and
must use :meth:`!object.__setattr__`. must use :meth:`!__setattr__`.
Inheritance Inheritance
----------- -----------
When the dataclass is being created by the :meth:`dataclass` decorator, When the dataclass is being created by the :func:`@dataclass <dataclass>` decorator,
it looks through all of the class's base classes in reverse MRO (that it looks through all of the class's base classes in reverse MRO (that
is, starting at :class:`object`) and, for each dataclass that it finds, is, starting at :class:`object`) and, for each dataclass that it finds,
adds the fields from that base class to an ordered mapping of fields. adds the fields from that base class to an ordered mapping of fields.
@ -641,8 +641,8 @@ The generated :meth:`~object.__init__` method for ``C`` will look like::
def __init__(self, x: int = 15, y: int = 0, z: int = 10): def __init__(self, x: int = 15, y: int = 0, z: int = 10):
Re-ordering of keyword-only parameters in :meth:`~object.__init__` Re-ordering of keyword-only parameters in :meth:`!__init__`
------------------------------------------------------------------ -----------------------------------------------------------
After the parameters needed for :meth:`~object.__init__` are computed, any After the parameters needed for :meth:`~object.__init__` are computed, any
keyword-only parameters are moved to come after all regular keyword-only parameters are moved to come after all regular
@ -665,7 +665,7 @@ fields, and ``Base.x`` and ``D.z`` are regular fields::
z: int = 10 z: int = 10
t: int = field(kw_only=True, default=0) t: int = field(kw_only=True, default=0)
The generated :meth:`~object.__init__` method for ``D`` will look like:: The generated :meth:`!__init__` method for ``D`` will look like::
def __init__(self, x: Any = 15.0, z: int = 10, *, y: int = 0, w: int = 1, t: int = 0): def __init__(self, x: Any = 15.0, z: int = 10, *, y: int = 0, w: int = 1, t: int = 0):
@ -674,7 +674,7 @@ the list of fields: parameters derived from regular fields are
followed by parameters derived from keyword-only fields. followed by parameters derived from keyword-only fields.
The relative ordering of keyword-only parameters is maintained in the The relative ordering of keyword-only parameters is maintained in the
re-ordered :meth:`~object.__init__` parameter list. re-ordered :meth:`!__init__` parameter list.
Default factory functions Default factory functions
@ -689,7 +689,7 @@ example, to create a new instance of a list, use::
If a field is excluded from :meth:`~object.__init__` (using ``init=False``) If a field is excluded from :meth:`~object.__init__` (using ``init=False``)
and the field also specifies ``default_factory``, then the default and the field also specifies ``default_factory``, then the default
factory function will always be called from the generated factory function will always be called from the generated
:meth:`~object.__init__` function. This happens because there is no other :meth:`!__init__` function. This happens because there is no other
way to give the field an initial value. way to give the field an initial value.
Mutable default values Mutable default values
@ -738,7 +738,7 @@ for ``x`` when creating a class instance will share the same copy
of ``x``. Because dataclasses just use normal Python class of ``x``. Because dataclasses just use normal Python class
creation they also share this behavior. There is no general way creation they also share this behavior. There is no general way
for Data Classes to detect this condition. Instead, the for Data Classes to detect this condition. Instead, the
:func:`dataclass` decorator will raise a :exc:`ValueError` if it :func:`@dataclass <dataclass>` decorator will raise a :exc:`ValueError` if it
detects an unhashable default parameter. The assumption is that if detects an unhashable default parameter. The assumption is that if
a value is unhashable, it is mutable. This is a partial solution, a value is unhashable, it is mutable. This is a partial solution,
but it does protect against many common errors. but it does protect against many common errors.
@ -764,15 +764,17 @@ Descriptor-typed fields
Fields that are assigned :ref:`descriptor objects <descriptors>` as their Fields that are assigned :ref:`descriptor objects <descriptors>` as their
default value have the following special behaviors: default value have the following special behaviors:
* The value for the field passed to the dataclass's ``__init__`` method is * The value for the field passed to the dataclass's :meth:`~object.__init__` method is
passed to the descriptor's ``__set__`` method rather than overwriting the passed to the descriptor's :meth:`~object.__set__` method rather than overwriting the
descriptor object. descriptor object.
* Similarly, when getting or setting the field, the descriptor's * Similarly, when getting or setting the field, the descriptor's
``__get__`` or ``__set__`` method is called rather than returning or :meth:`~object.__get__` or :meth:`!__set__` method is called rather than returning or
overwriting the descriptor object. overwriting the descriptor object.
* To determine whether a field contains a default value, ``dataclasses``
will call the descriptor's ``__get__`` method using its class access * To determine whether a field contains a default value, :func:`@dataclass <dataclass>`
form (i.e. ``descriptor.__get__(obj=None, type=cls)``. If the will call the descriptor's :meth:`!__get__` method using its class access
form: ``descriptor.__get__(obj=None, type=cls)``. If the
descriptor returns a value in this case, it will be used as the descriptor returns a value in this case, it will be used as the
field's default. On the other hand, if the descriptor raises field's default. On the other hand, if the descriptor raises
:exc:`AttributeError` in this situation, no default value will be :exc:`AttributeError` in this situation, no default value will be