From e01831760e3c7cb9cdba78b048c8052808a3a663 Mon Sep 17 00:00:00 2001 From: "Erlend E. Aasland" Date: Sun, 14 Apr 2024 18:29:01 +0200 Subject: Doc: mark up classes, attributes, parameters, and methods in dataclasses.rst (#117820) --- Doc/library/dataclasses.rst | 170 ++++++++++++++++++++++---------------------- 1 file changed, 85 insertions(+), 85 deletions(-) diff --git a/Doc/library/dataclasses.rst b/Doc/library/dataclasses.rst index 70aaaa5..7a8b83e 100644 --- a/Doc/library/dataclasses.rst +++ b/Doc/library/dataclasses.rst @@ -12,7 +12,7 @@ -------------- This module provides a decorator and functions for automatically -adding generated :term:`special method`\s such as :meth:`~object.__init__` and +adding generated :term:`special methods ` such as :meth:`~object.__init__` and :meth:`~object.__repr__` to user-defined classes. It was originally described in :pep:`557`. @@ -39,7 +39,7 @@ will add, among other things, a :meth:`!__init__` that looks like:: self.quantity_on_hand = quantity_on_hand Note that this method is automatically added to the class: it is not -directly specified in the ``InventoryItem`` definition shown above. +directly specified in the :class:`!InventoryItem` definition shown above. .. versionadded:: 3.7 @@ -86,13 +86,13 @@ Module contents 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. If the class already defines :meth:`!__init__`, this parameter is 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 generated. The generated repr string will have the class name and the name and repr of each field, in the order they are defined in the class. Fields that are marked as being excluded from the repr @@ -102,7 +102,7 @@ Module contents If the class already defines :meth:`!__repr__`, this parameter is 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 generated. This method compares the class as if it were a tuple of its fields, in order. Both instances in the comparison must be of the identical type. @@ -110,26 +110,26 @@ Module contents If the class already defines :meth:`!__eq__`, this parameter is ignored. - - ``order``: If true (the default is ``False``), :meth:`~object.__lt__`, + - *order*: If true (the default is ``False``), :meth:`~object.__lt__`, :meth:`~object.__le__`, :meth:`~object.__gt__`, and :meth:`~object.__ge__` methods will be generated. These compare the class as if it were a tuple of its fields, in order. Both instances in the comparison must be of the - 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. If the class already defines any of :meth:`!__lt__`, :meth:`!__le__`, :meth:`!__gt__`, or :meth:`!__ge__`, then :exc:`TypeError` is raised. - - ``unsafe_hash``: If ``False`` (the default), a :meth:`~object.__hash__` method - is generated according to how ``eq`` and ``frozen`` are set. + - *unsafe_hash*: If ``False`` (the default), a :meth:`~object.__hash__` method + is generated according to how *eq* and *frozen* are set. :meth:`!__hash__` is used by built-in :meth:`hash()`, and when objects are added to hashed collections such as dictionaries and sets. Having a :meth:`!__hash__` implies that instances of the class are immutable. Mutability is a complicated property that depends on the programmer's intent, the existence and behavior of :meth:`!__eq__`, and the values of - the ``eq`` and ``frozen`` flags in the ``@dataclass`` decorator. + the *eq* and *frozen* flags in the ``@dataclass`` decorator. 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 @@ -149,29 +149,29 @@ Module contents method in your dataclass and set ``unsafe_hash=True``; this will result in a :exc:`TypeError`. - If ``eq`` and ``frozen`` are both true, by default ``@dataclass`` will - generate a :meth:`!__hash__` method for you. If ``eq`` is true and - ``frozen`` is false, :meth:`!__hash__` will be set to ``None``, marking it - unhashable (which it is, since it is mutable). If ``eq`` is false, + If *eq* and *frozen* are both true, by default ``@dataclass`` will + generate a :meth:`!__hash__` method for you. If *eq* is true and + *frozen* is false, :meth:`!__hash__` will be set to ``None``, marking it + unhashable (which it is, since it is mutable). If *eq* is false, :meth:`!__hash__` will be left untouched meaning the :meth:`!__hash__` method of the superclass will be used (if the superclass is :class:`object`, this means it will fall back to id-based hashing). - - ``frozen``: If true (the default is ``False``), assigning to fields will + - *frozen*: If true (the default is ``False``), assigning to fields will generate an exception. This emulates read-only frozen instances. If :meth:`~object.__setattr__` or :meth:`~object.__delattr__` is defined in the class, then :exc:`TypeError` is raised. See the discussion below. - - ``match_args``: If true (the default is ``True``), the - ``__match_args__`` tuple will be created from the list of + - *match_args*: If true (the default is ``True``), the + :attr:`~object.__match_args__` tuple will be created from the list of parameters to the generated :meth:`~object.__init__` method (even if :meth:`!__init__` is not generated, see above). If false, or if - ``__match_args__`` is already defined in the class, then - ``__match_args__`` will not be generated. + :attr:`!__match_args__` is already defined in the class, then + :attr:`!__match_args__` will not be generated. .. versionadded:: 3.10 - - ``kw_only``: If true (the default value is ``False``), then all + - *kw_only*: If true (the default value is ``False``), then all 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__` parameter generated from a keyword-only field must be specified @@ -182,7 +182,7 @@ Module contents .. versionadded:: 3.10 - - ``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. If :attr:`!__slots__` is already defined in the class, then :exc:`TypeError` is raised. @@ -190,16 +190,16 @@ Module contents .. versionadded:: 3.10 .. versionchanged:: 3.11 - If a field name is already included in the ``__slots__`` - of a base class, it will not be included in the generated ``__slots__`` + If a field name is already included in the :attr:`!__slots__` + of a base class, it will not be included in the generated :attr:`!__slots__` to prevent :ref:`overriding them `. - Therefore, do not use ``__slots__`` to retrieve the field names of a + Therefore, do not use :attr:`!__slots__` to retrieve the field names of a dataclass. Use :func:`fields` instead. To be able to determine inherited slots, - base class ``__slots__`` may be any iterable, but *not* an iterator. + base class :attr:`!__slots__` may be any iterable, but *not* an iterator. - - ``weakref_slot``: If true (the default is ``False``), add a slot + - *weakref_slot*: If true (the default is ``False``), add a slot named "__weakref__", which is required to make an instance weakref-able. It is an error to specify ``weakref_slot=True`` without also specifying ``slots=True``. @@ -214,7 +214,7 @@ Module contents a: int # 'a' has no default value b: int = 0 # assign a default value for 'b' - In this example, both ``a`` and ``b`` will be included in the added + In this example, both :attr:`!a` and :attr:`!b` will be included in the added :meth:`~object.__init__` method, which will be defined as:: def __init__(self, a: int, b: int = 0): @@ -245,25 +245,25 @@ Module contents 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 :func:`!field` call itself 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 callable that will be called when a default value is needed for this field. Among other purposes, this can be used to specify fields with mutable default values, as discussed below. It is an - error to specify both ``default`` and ``default_factory``. + error to specify both *default* and *default_factory*. - - ``init``: If true (the default), this field is included as a + - *init*: If true (the default), this field is included as a parameter to the generated :meth:`~object.__init__` method. - - ``repr``: If true (the default), this field is included in the + - *repr*: If true (the default), this field is included in the string returned by the generated :meth:`~object.__repr__` method. - - ``hash``: This can be a bool or ``None``. If true, this field is + - *hash*: This can be a bool or ``None``. If true, this field is included in the generated :meth:`~object.__hash__` method. If ``None`` (the - default), use the value of ``compare``: this would normally be + default), use the value of *compare*: this would normally be the expected behavior. A field should be considered in the hash if it's used for comparisons. Setting this value to anything other than ``None`` is discouraged. @@ -274,11 +274,11 @@ Module contents fields that contribute to the type's hash value. Even if a field is excluded from the hash, it will still be used for comparisons. - - ``compare``: If true (the default), this field is included in the + - *compare*: If true (the default), this field is included in the generated equality and comparison methods (:meth:`~object.__eq__`, :meth:`~object.__gt__`, et al.). - - ``metadata``: This can be a mapping or None. None is treated as + - *metadata*: This can be a mapping or None. None is treated as an empty dict. This value is wrapped in :func:`~types.MappingProxyType` to make it read-only, and exposed on the :class:`Field` object. It is not used at all by Data @@ -286,7 +286,7 @@ Module contents Multiple third-parties can each have their own key, to use as a namespace in the metadata. - - ``kw_only``: If true, this field will be marked as keyword-only. + - *kw_only*: If true, this field will be marked as keyword-only. This is used when the generated :meth:`~object.__init__` method's parameters are computed. @@ -294,7 +294,7 @@ Module contents If the default value of a field is specified by a call to :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 *default* is not provided, then the class attribute will be deleted. The intent is that after the :func:`@dataclass ` decorator runs, the class attributes will all contain the default values for the fields, just @@ -308,9 +308,9 @@ Module contents z: int = field(repr=False, default=10) t: int = 20 - The class attribute ``C.z`` will be ``10``, the class attribute - ``C.t`` will be ``20``, and the class attributes ``C.x`` and - ``C.y`` will not be set. + The class attribute :attr:`!C.z` will be ``10``, the class attribute + :attr:`!C.t` will be ``20``, and the class attributes :attr:`!C.x` and + :attr:`!C.y` will not be set. .. class:: Field @@ -319,10 +319,10 @@ Module contents module-level method (see below). Users should never instantiate a :class:`!Field` object directly. Its documented attributes are: - - ``name``: The name of the field. - - ``type``: The type of the field. - - ``default``, ``default_factory``, ``init``, ``repr``, ``hash``, - ``compare``, ``metadata``, and ``kw_only`` have the identical + - :attr:`!name`: The name of the field. + - :attr:`!type`: The type of the field. + - :attr:`!default`, :attr:`!default_factory`, :attr:`!init`, :attr:`!repr`, :attr:`!hash`, + :attr:`!compare`, :attr:`!metadata`, and :attr:`!kw_only` have the identical meaning and values as they do in the :func:`field` function. Other attributes may exist, but they are private and must not be @@ -337,8 +337,8 @@ Module contents .. function:: asdict(obj, *, dict_factory=dict) - Converts the dataclass ``obj`` to a dict (by using the - factory function ``dict_factory``). Each dataclass is converted + Converts the dataclass *obj* to a dict (by using the + factory function *dict_factory*). Each dataclass is converted to a dict of its fields, as ``name: value`` pairs. dataclasses, dicts, lists, and tuples are recursed into. Other objects are copied with :func:`copy.deepcopy`. @@ -364,13 +364,13 @@ Module contents {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. .. function:: astuple(obj, *, tuple_factory=tuple) - Converts the dataclass ``obj`` to a tuple (by using the - factory function ``tuple_factory``). Each dataclass is converted + Converts the dataclass *obj* to a tuple (by using the + factory function *tuple_factory*). Each dataclass is converted to a tuple of its field values. dataclasses, dicts, lists, and tuples are recursed into. Other objects are copied with :func:`copy.deepcopy`. @@ -384,28 +384,28 @@ Module contents 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. .. 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) - Creates a new dataclass with name ``cls_name``, fields as defined - in ``fields``, base classes as given in ``bases``, and initialized - with a namespace as given in ``namespace``. ``fields`` is an + Creates a new dataclass with name *cls_name*, fields as defined + in *fields*, base classes as given in *bases*, and initialized + with a namespace as given in *namespace*. *fields* is an iterable whose elements are each either ``name``, ``(name, type)``, or ``(name, type, Field)``. If just ``name`` is supplied, - ``typing.Any`` is used for ``type``. The values of ``init``, - ``repr``, ``eq``, ``order``, ``unsafe_hash``, ``frozen``, - ``match_args``, ``kw_only``, ``slots``, and ``weakref_slot`` have + :data:`typing.Any` is used for ``type``. The values of *init*, + *repr*, *eq*, *order*, *unsafe_hash*, *frozen*, + *match_args*, *kw_only*, *slots*, and *weakref_slot* have the same meaning as they do in :func:`@dataclass `. - If ``module`` is defined, the ``__module__`` attribute + If *module* is defined, the :attr:`!__module__` attribute of the dataclass is set to that value. By default, it is set to the module name of the caller. This function is not strictly required, because any Python - mechanism for creating a new class with ``__annotations__`` can - then apply the ``@dataclass`` function to convert that class to + mechanism for creating a new class with :attr:`!__annotations__` can + then apply the :func:`@dataclass ` function to convert that class to a dataclass. This function is provided as a convenience. For example:: @@ -428,9 +428,9 @@ Module contents .. function:: replace(obj, /, **changes) - Creates a new object of the same type as ``obj``, replacing - fields with values from ``changes``. If ``obj`` is not a Data - Class, raises :exc:`TypeError`. If keys in ``changes`` are not + Creates a new object of the same type as *obj*, replacing + fields with values from *changes*. If *obj* is not a Data + Class, raises :exc:`TypeError`. If keys in *changes* are not field names of the given dataclass, raises :exc:`TypeError`. The newly returned object is created by calling the :meth:`~object.__init__` @@ -441,7 +441,7 @@ Module contents specified on the call to :func:`!replace` so that they can be passed to :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 in this case. @@ -451,7 +451,7 @@ Module contents initialized at all. It is expected that ``init=False`` fields will be rarely and judiciously used. If they are used, it might be wise to have alternate class constructors, or perhaps a custom - ``replace()`` (or similarly named) method which handles instance + :func:`!replace` (or similarly named) method which handles instance copying. Dataclass instances are also supported by generic function :func:`copy.replace`. @@ -513,7 +513,7 @@ Post-init processing .. function:: __post_init__() 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 :meth:`!self.__post_init__`. However, if any ``InitVar`` fields are defined, they will also be passed to :meth:`!__post_init__` in the order they were defined in the class. If no :meth:`!__init__` method is generated, then @@ -564,7 +564,7 @@ Class variables One of the few places where :func:`@dataclass ` actually inspects the type 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 -``typing.ClassVar``. If a field is a ``ClassVar``, it is excluded +:data:`typing.ClassVar`. If a field is a ``ClassVar``, it is excluded from consideration as a field and is ignored by the dataclass mechanisms. Such ``ClassVar`` pseudo-fields are not returned by the module-level :func:`fields` function. @@ -599,8 +599,8 @@ value is not provided when creating the class:: c = C(10, database=my_database) -In this case, :func:`fields` will return :class:`Field` objects for ``i`` and -``j``, but not for ``database``. +In this case, :func:`fields` will return :class:`Field` objects for :attr:`!i` and +:attr:`!j`, but not for :attr:`!database`. .. _dataclasses-frozen: @@ -642,10 +642,10 @@ example:: z: int = 10 x: int = 15 -The final list of fields is, in order, ``x``, ``y``, ``z``. The final -type of ``x`` is ``int``, as specified in class ``C``. +The final list of fields is, in order, :attr:`!x`, :attr:`!y`, :attr:`!z`. The final +type of :attr:`!x` is :class:`int`, as specified in class :class:`!C`. -The generated :meth:`~object.__init__` method for ``C`` will look like:: +The generated :meth:`~object.__init__` method for :class:`!C` will look like:: def __init__(self, x: int = 15, y: int = 0, z: int = 10): @@ -658,8 +658,8 @@ keyword-only parameters are moved to come after all regular keyword-only parameters are implemented in Python: they must come after non-keyword-only parameters. -In this example, ``Base.y``, ``Base.w``, and ``D.t`` are keyword-only -fields, and ``Base.x`` and ``D.z`` are regular fields:: +In this example, :attr:`!Base.y`, :attr:`!Base.w`, and :attr:`!D.t` are keyword-only +fields, and :attr:`!Base.x` and :attr:`!D.z` are regular fields:: @dataclass class Base: @@ -673,7 +673,7 @@ fields, and ``Base.x`` and ``D.z`` are regular fields:: z: int = 10 t: int = field(kw_only=True, default=0) -The generated :meth:`!__init__` method for ``D`` will look like:: +The generated :meth:`!__init__` method for :class:`!D` will look like:: def __init__(self, x: Any = 15.0, z: int = 10, *, y: int = 0, w: int = 1, t: int = 0): @@ -688,14 +688,14 @@ re-ordered :meth:`!__init__` parameter list. Default factory functions ------------------------- -If a :func:`field` specifies a ``default_factory``, it is called with +If a :func:`field` specifies a *default_factory*, it is called with zero arguments when a default value for the field is needed. For example, to create a new instance of a list, use:: mylist: list = field(default_factory=list) 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 :meth:`!__init__` function. This happens because there is no other way to give the field an initial value. @@ -718,8 +718,8 @@ Consider this example, not using dataclasses:: assert o1.x == [1, 2] assert o1.x is o2.x -Note that the two instances of class ``C`` share the same class -variable ``x``, as expected. +Note that the two instances of class :class:`!C` share the same class +variable :attr:`!x`, as expected. Using dataclasses, *if* this code was valid:: @@ -740,10 +740,10 @@ it would generate code similar to:: assert D().x is D().x -This has the same issue as the original example using class ``C``. -That is, two instances of class ``D`` that do not specify a value -for ``x`` when creating a class instance will share the same copy -of ``x``. Because dataclasses just use normal Python class +This has the same issue as the original example using class :class:`!C`. +That is, two instances of class :class:`!D` that do not specify a value +for :attr:`!x` when creating a class instance will share the same copy +of :attr:`!x`. Because dataclasses just use normal Python class creation they also share this behavior. There is no general way for Data Classes to detect this condition. Instead, the :func:`@dataclass ` decorator will raise a :exc:`ValueError` if it @@ -761,8 +761,8 @@ mutable types as default values for fields:: assert D().x is not D().x .. versionchanged:: 3.11 - Instead of looking for and disallowing objects of type ``list``, - ``dict``, or ``set``, unhashable objects are now not allowed as + Instead of looking for and disallowing objects of type :class:`list`, + :class:`dict`, or :class:`set`, unhashable objects are now not allowed as default values. Unhashability is used to approximate mutability. -- cgit v0.12