221 lines
6.5 KiB
ReStructuredText
221 lines
6.5 KiB
ReStructuredText
:mod:`types` --- Dynamic type creation and names for built-in types
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===================================================================
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.. module:: types
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:synopsis: Names for built-in types.
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**Source code:** :source:`Lib/types.py`
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--------------
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This module defines utility function to assist in dynamic creation of
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new types.
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It also defines names for some object types that are used by the standard
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Python interpreter, but not exposed as builtins like :class:`int` or
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:class:`str` are.
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Dynamic Type Creation
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---------------------
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.. function:: new_class(name, bases=(), kwds=None, exec_body=None)
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Creates a class object dynamically using the appropriate metaclass.
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The first three arguments are the components that make up a class
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definition header: the class name, the base classes (in order), the
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keyword arguments (such as ``metaclass``).
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The *exec_body* argument is a callback that is used to populate the
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freshly created class namespace. It should accept the class namespace
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as its sole argument and update the namespace directly with the class
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contents. If no callback is provided, it has the same effect as passing
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in ``lambda ns: ns``.
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.. versionadded:: 3.3
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.. function:: prepare_class(name, bases=(), kwds=None)
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Calculates the appropriate metaclass and creates the class namespace.
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The arguments are the components that make up a class definition header:
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the class name, the base classes (in order) and the keyword arguments
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(such as ``metaclass``).
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The return value is a 3-tuple: ``metaclass, namespace, kwds``
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*metaclass* is the appropriate metaclass, *namespace* is the
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prepared class namespace and *kwds* is an updated copy of the passed
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in *kwds* argument with any ``'metaclass'`` entry removed. If no *kwds*
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argument is passed in, this will be an empty dict.
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.. versionadded:: 3.3
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.. seealso::
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:ref:`metaclasses`
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Full details of the class creation process supported by these functions
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:pep:`3115` - Metaclasses in Python 3000
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Introduced the ``__prepare__`` namespace hook
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Standard Interpreter Types
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--------------------------
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This module provides names for many of the types that are required to
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implement a Python interpreter. It deliberately avoids including some of
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the types that arise only incidentally during processing such as the
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``listiterator`` type.
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Typical use is of these names is for :func:`isinstance` or
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:func:`issubclass` checks.
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Standard names are defined for the following types:
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.. data:: FunctionType
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LambdaType
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The type of user-defined functions and functions created by
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:keyword:`lambda` expressions.
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.. data:: GeneratorType
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The type of :term:`generator`-iterator objects, produced by calling a
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generator function.
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.. data:: CodeType
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.. index:: builtin: compile
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The type for code objects such as returned by :func:`compile`.
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.. data:: MethodType
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The type of methods of user-defined class instances.
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.. data:: BuiltinFunctionType
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BuiltinMethodType
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The type of built-in functions like :func:`len` or :func:`sys.exit`, and
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methods of built-in classes. (Here, the term "built-in" means "written in
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C".)
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.. data:: ModuleType
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The type of modules.
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.. data:: TracebackType
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The type of traceback objects such as found in ``sys.exc_info()[2]``.
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.. data:: FrameType
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The type of frame objects such as found in ``tb.tb_frame`` if ``tb`` is a
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traceback object.
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.. data:: GetSetDescriptorType
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The type of objects defined in extension modules with ``PyGetSetDef``, such
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as ``FrameType.f_locals`` or ``array.array.typecode``. This type is used as
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descriptor for object attributes; it has the same purpose as the
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:class:`property` type, but for classes defined in extension modules.
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.. data:: MemberDescriptorType
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The type of objects defined in extension modules with ``PyMemberDef``, such
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as ``datetime.timedelta.days``. This type is used as descriptor for simple C
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data members which use standard conversion functions; it has the same purpose
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as the :class:`property` type, but for classes defined in extension modules.
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.. impl-detail::
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In other implementations of Python, this type may be identical to
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``GetSetDescriptorType``.
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.. class:: MappingProxyType(mapping)
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Read-only proxy of a mapping. It provides a dynamic view on the mapping's
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entries, which means that when the mapping changes, the view reflects these
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changes.
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.. versionadded:: 3.3
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.. describe:: key in proxy
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Return ``True`` if the underlying mapping has a key *key*, else
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``False``.
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.. describe:: proxy[key]
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Return the item of the underlying mapping with key *key*. Raises a
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:exc:`KeyError` if *key* is not in the underlying mapping.
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.. describe:: iter(proxy)
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Return an iterator over the keys of the underlying mapping. This is a
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shortcut for ``iter(proxy.keys())``.
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.. describe:: len(proxy)
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Return the number of items in the underlying mapping.
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.. method:: copy()
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Return a shallow copy of the underlying mapping.
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.. method:: get(key[, default])
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Return the value for *key* if *key* is in the underlying mapping, else
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*default*. If *default* is not given, it defaults to ``None``, so that
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this method never raises a :exc:`KeyError`.
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.. method:: items()
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Return a new view of the underlying mapping's items (``(key, value)``
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pairs).
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.. method:: keys()
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Return a new view of the underlying mapping's keys.
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.. method:: values()
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Return a new view of the underlying mapping's values.
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.. class:: SimpleNamespace
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A simple :class:`object` subclass that provides attribute access to its
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namespace, as well as a meaningful repr.
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Unlike :class:`object`, with ``SimpleNamespace`` you can add and remove
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attributes. If a ``SimpleNamespace`` object is initialized with keyword
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arguments, those are directly added to the underlying namespace.
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The type is roughly equivalent to the following code::
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class SimpleNamespace:
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def __init__(self, **kwargs):
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self.__dict__.update(kwargs)
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def __repr__(self):
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keys = sorted(self.__dict__)
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items = ("{}={!r}".format(k, self.__dict__[k]) for k in keys)
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return "{}({})".format(type(self).__name__, ", ".join(items))
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``SimpleNamespace`` may be useful as a replacement for ``class NS: pass``.
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However, for a structured record type use :func:`~collections.namedtuple`
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instead.
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.. versionadded:: 3.3
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