types — Dynamic type creation and names for built-in types — Python 3.12.9 documentation
Description: Source code: Lib/types.py This module defines utility functions to assist in dynamic creation of new types. It also defines names for some object types that are used by the standard Python interpre...

# `types` — Dynamic type creation and names for built-in types

Source code: Lib/types.py

This module defines utility functions to assist in dynamic creation of new types.

It also defines names for some object types that are used by the standard Python interpreter, but not exposed as builtins like `int` or `str` are.

Finally, it provides some additional type-related utility classes and functions that are not fundamental enough to be builtins.

## Dynamic Type Creation

types.new_class(name, bases=(), kwds=None, exec_body=None)

  Creates a class object dynamically using the appropriate metaclass.

  The first three arguments are the components that make up a class definition header: the class name, the base classes (in order), the keyword arguments (such as `metaclass`).

  The exec_body argument is a callback that is used to populate the freshly created class namespace. It should accept the class namespace as its sole argument and update the namespace directly with the class contents. If no callback is provided, it has the same effect as passing in `lambda ns: None`.

  Added in version 3.3.

types.prepare_class(name, bases=(), kwds=None)

  Calculates the appropriate metaclass and creates the class namespace.

  The arguments are the components that make up a class definition header: the class name, the base classes (in order) and the keyword arguments (such as `metaclass`).

  The return value is a 3-tuple: `metaclass, namespace, kwds`

  metaclass is the appropriate metaclass, namespace is the prepared class namespace and kwds is an updated copy of the passed in kwds argument with any `'metaclass'` entry removed. If no kwds argument is passed in, this will be an empty dict.

  Added in version 3.3.

  Changed in version 3.6: The default value for the `namespace` element of the returned tuple has changed. Now an insertion-order-preserving mapping is used when the metaclass does not have a `__prepare__` method.

See also

Metaclasses

  Full details of the class creation process supported by these functions

PEP 3115 - Metaclasses in Python 3000

  Introduced the `__prepare__` namespace hook

types.resolve_bases(bases)

  Resolve MRO entries dynamically as specified by PEP 560.

  This function looks for items in bases that are not instances of `type`, and returns a tuple where each such object that has an `__mro_entries__()` method is replaced with an unpacked result of calling this method. If a bases item is an instance of `type`, or it doesn’t have an `__mro_entries__()` method, then it is included in the return tuple unchanged.

  Added in version 3.7.

types.get_original_bases(cls, /)

  Return the tuple of objects originally given as the bases of cls before the `__mro_entries__()` method has been called on any bases (following the mechanisms laid out in PEP 560). This is useful for introspecting Generics.

  For classes that have an `__orig_bases__` attribute, this function returns the value of `cls.__orig_bases__`. For classes without the `__orig_bases__` attribute, `cls.__bases__` is returned.

  Examples:

      from typing import TypeVar, Generic, NamedTuple, TypedDict

      T = TypeVar("T")
      class Foo(Generic[T]): ...
      class Bar(Foo[int], float): ...
      class Baz(list[str]): ...
      Eggs = NamedTuple("Eggs", [("a", int), ("b", str)])
      Spam = TypedDict("Spam", {"a": int, "b": str})

      assert Bar.__bases__ == (Foo, float)
      assert get_original_bases(Bar) == (Foo[int], float)

      assert Baz.__bases__ == (list,)
      assert get_original_bases(Baz) == (list[str],)

      assert Eggs.__bases__ == (tuple,)
      assert get_original_bases(Eggs) == (NamedTuple,)

      assert Spam.__bases__ == (dict,)
      assert get_original_bases(Spam) == (TypedDict,)

      assert int.__bases__ == (object,)
      assert get_original_bases(int) == (object,)

  Added in version 3.12.

See also

PEP 560 - Core support for typing module and generic types

## Standard Interpreter Types

This module provides names for many of the types that are required to implement a Python interpreter. It deliberately avoids including some of the types that arise only incidentally during processing such as the `listiterator` type.

Typical use of these names is for `isinstance()` or `issubclass()` checks.

If you instantiate any of these types, note that signatures may vary between Python versions.

Standard names are defined for the following types:

types.NoneType

  The type of `None`.

  Added in version 3.10.

types.FunctionType
types.LambdaType

  The type of user-defined functions and functions created by `lambda` expressions.

  Raises an auditing event `function.__new__` with argument `code`.

  The audit event only occurs for direct instantiation of function objects, and is not raised for normal compilation.

types.GeneratorType

  The type of generator-iterator objects, created by generator functions.

types.CoroutineType

  The type of coroutine objects, created by `async def` functions.

  Added in version 3.5.

types.AsyncGeneratorType

  The type of asynchronous generator-iterator objects, created by asynchronous generator functions.

  Added in version 3.6.

class types.CodeType(**kwargs)

  The type of code objects such as returned by `compile()`.

  Raises an auditing event `code.__new__` with arguments `code`, `filename`, `name`, `argcount`, `posonlyargcount`, `kwonlyargcount`, `nlocals`, `stacksize`, `flags`.

  Note that the audited arguments may not match the names or positions required by the initializer. The audit event only occurs for direct instantiation of code objects, and is not raised for normal compilation.

types.CellType

  The type for cell objects: such objects are used as containers for a function’s free variables.

  Added in version 3.8.

types.MethodType

  The type of methods of user-defined class instances.

types.BuiltinFunctionType
types.BuiltinMethodType

  The type of built-in functions like `len()` or `sys.exit()`, and methods of built-in classes. (Here, the term “built-in” means “written in C”.)

types.WrapperDescriptorType

  The type of methods of some built-in data types and base classes such as `object.__init__()` or `object.__lt__()`.

  Added in version 3.7.

types.MethodWrapperType

  The type of bound methods of some built-in data types and base classes. For example it is the type of `object().__str__`.

  Added in version 3.7.

types.NotImplementedType

  The type of `NotImplemented`.

  Added in version 3.10.

types.MethodDescriptorType

  The type of methods of some built-in data types such as `str.join()`.

  Added in version 3.7.

types.ClassMethodDescriptorType

  The type of unbound class methods of some built-in data types such as `dict.__dict__['fromkeys']`.

  Added in version 3.7.

class types.ModuleType(name, doc=None)

  The type of modules. The constructor takes the name of the module to be created and optionally its docstring.

  See also

  Documentation on module objects

    Provides details on the special attributes that can be found on instances of `ModuleType`.

  `importlib.util.module_from_spec()`

    Modules created using the `ModuleType` constructor are created with many of their special attributes unset or set to default values. `module_from_spec()` provides a more robust way of creating `ModuleType` instances which ensures the various attributes are set appropriately.

types.EllipsisType

  The type of `Ellipsis`.

  Added in version 3.10.

class types.GenericAlias(t_origin, t_args)

  The type of parameterized generics such as `list[int]`.

  `t_origin` should be a non-parameterized generic class, such as `list`, `tuple` or `dict`. `t_args` should be a `tuple` (possibly of length 1) of types which parameterize `t_origin`:

      >>> from types import GenericAlias

      >>> list[int] == GenericAlias(list, (int,))
      True
      >>> dict[str, int] == GenericAlias(dict, (str, int))
      True

  Added in version 3.9.

  Changed in version 3.9.2: This type can now be subclassed.

  See also

  Generic Alias Types

    In-depth documentation on instances of `types.GenericAlias`

  PEP 585 - Type Hinting Generics In Standard Collections

    Introducing the `types.GenericAlias` class

class types.UnionType

  The type of union type expressions.

  Added in version 3.10.

class types.TracebackType(tb_next, tb_frame, tb_lasti, tb_lineno)

  The type of traceback objects such as found in `sys.exception().__traceback__`.

  See the language reference for details of the available attributes and operations, and guidance on creating tracebacks dynamically.

types.FrameType

  The type of frame objects such as found in `tb.tb_frame` if `tb` is a traceback object.

types.GetSetDescriptorType

  The type of objects defined in extension modules with `PyGetSetDef`, such as `FrameType.f_locals` or `array.array.typecode`. This type is used as descriptor for object attributes; it has the same purpose as the `property` type, but for classes defined in extension modules.

types.MemberDescriptorType

  The type of objects defined in extension modules with `PyMemberDef`, such as `datetime.timedelta.days`. This type is used as descriptor for simple C data members which use standard conversion functions; it has the same purpose as the `property` type, but for classes defined in extension modules.

  In addition, when a class is defined with a `__slots__` attribute, then for each slot, an instance of `MemberDescriptorType` will be added as an attribute on the class. This allows the slot to appear in the class’s `__dict__`.

  CPython implementation detail: In other implementations of Python, this type may be identical to `GetSetDescriptorType`.

class types.MappingProxyType(mapping)

  Read-only proxy of a mapping. It provides a dynamic view on the mapping’s entries, which means that when the mapping changes, the view reflects these changes.

  Added in version 3.3.

  Changed in version 3.9: Updated to support the new union (`|`) operator from PEP 584, which simply delegates to the underlying mapping.

  key in proxy

    Return `True` if the underlying mapping has a key key, else `False`.

  proxy[key]

    Return the item of the underlying mapping with key key. Raises a `KeyError` if key is not in the underlying mapping.

  iter(proxy)

    Return an iterator over the keys of the underlying mapping. This is a shortcut for `iter(proxy.keys())`.

  len(proxy)

    Return the number of items in the underlying mapping.

  copy()

    Return a shallow copy of the underlying mapping.

  get(key[, default])

    Return the value for key if key is in the underlying mapping, else default. If default is not given, it defaults to `None`, so that this method never raises a `KeyError`.

  items()

    Return a new view of the underlying mapping’s items (`(key, value)` pairs).

  keys()

    Return a new view of the underlying mapping’s keys.

  values()

    Return a new view of the underlying mapping’s values.

  reversed(proxy)

    Return a reverse iterator over the keys of the underlying mapping.

    Added in version 3.9.

  hash(proxy)

    Return a hash of the underlying mapping.

    Added in version 3.12.

## Additional Utility Classes and Functions

class types.SimpleNamespace

  A simple `object` subclass that provides attribute access to its namespace, as well as a meaningful repr.

  Unlike `object`, with `SimpleNamespace` you can add and remove attributes. If a `SimpleNamespace` object is initialized with keyword arguments, those are directly added to the underlying namespace.

  The type is roughly equivalent to the following code:

      class SimpleNamespace:
          def __init__(self, /, **kwargs):
              self.__dict__.update(kwargs)

          def __repr__(self):
              items = (f"{k}={v!r}" for k, v in self.__dict__.items())
              return "{}({})".format(type(self).__name__, ", ".join(items))

          def __eq__(self, other):
              if isinstance(self, SimpleNamespace) and isinstance(other, SimpleNamespace):
                 return self.__dict__ == other.__dict__
              return NotImplemented

  `SimpleNamespace` may be useful as a replacement for `class NS: pass`. However, for a structured record type use `namedtuple()` instead.

  Added in version 3.3.

  Changed in version 3.9: Attribute order in the repr changed from alphabetical to insertion (like `dict`).

types.DynamicClassAttribute(fget=None, fset=None, fdel=None, doc=None)

  Route attribute access on a class to __getattr__.

  This is a descriptor, used to define attributes that act differently when accessed through an instance and through a class. Instance access remains normal, but access to an attribute through a class will be routed to the class’s __getattr__ method; this is done by raising AttributeError.

  This allows one to have properties active on an instance, and have virtual attributes on the class with the same name (see `enum.Enum` for an example).

  Added in version 3.4.

## Coroutine Utility Functions

types.coroutine(gen_func)

  This function transforms a generator function into a coroutine function which returns a generator-based coroutine. The generator-based coroutine is still a generator iterator, but is also considered to be a coroutine object and is awaitable. However, it may not necessarily implement the `__await__()` method.

  If gen_func is a generator function, it will be modified in-place.

  If gen_func is not a generator function, it will be wrapped. If it returns an instance of `collections.abc.Generator`, the instance will be wrapped in an awaitable proxy object. All other types of objects will be returned as is.

  Added in version 3.5.