types — Dynamic type creation and names for built-in types — Python 3.9.22 documentation

# `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`.

  New 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.

  New 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.

  New in version 3.7.

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.` `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.

  New in version 3.5.

`types.` `AsyncGeneratorType`

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

  New in version 3.6.

class `types.` `CodeType`(**kwargs)

  The type for 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.

  `replace`(**kwargs)

    Return a copy of the code object with new values for the specified fields.

    New in version 3.8.

`types.` `CellType`

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

  New 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__()`.

  New 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__`.

  New in version 3.7.

`types.` `MethodDescriptorType`

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

  New in version 3.7.

`types.` `ClassMethodDescriptorType`

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

  New 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.

  Note

  Use `importlib.util.module_from_spec()` to create a new module if you wish to set the various import-controlled attributes.

  `__doc__`

    The docstring of the module. Defaults to `None`.

  `__loader__`

    The loader which loaded the module. Defaults to `None`.

    This attribute is to match `importlib.machinery.ModuleSpec.loader` as stored in the attr:__spec__ object.

    Note

    A future version of Python may stop setting this attribute by default. To guard against this potential change, preferably read from the `__spec__` attribute instead or use `getattr(module, "__loader__", None)` if you explicitly need to use this attribute.

    Changed in version 3.4: Defaults to `None`. Previously the attribute was optional.

  `__name__`

    The name of the module. Expected to match `importlib.machinery.ModuleSpec.name`.

  `__package__`

    Which package a module belongs to. If the module is top-level (i.e. not a part of any specific package) then the attribute should be set to `''`, else it should be set to the name of the package (which can be `__name__` if the module is a package itself). Defaults to `None`.

    This attribute is to match `importlib.machinery.ModuleSpec.parent` as stored in the attr:__spec__ object.

    Note

    A future version of Python may stop setting this attribute by default. To guard against this potential change, preferably read from the `__spec__` attribute instead or use `getattr(module, "__package__", None)` if you explicitly need to use this attribute.

    Changed in version 3.4: Defaults to `None`. Previously the attribute was optional.

  `__spec__`

    A record of the module’s import-system-related state. Expected to be an instance of `importlib.machinery.ModuleSpec`.

    New in version 3.4.

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

  New in version 3.9.

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

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

  The type of traceback objects such as found in `sys.exc_info()[2]`.

  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.

  See the language reference for details of the available attributes and operations.

`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.

  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.

  New 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.

    New in version 3.9.

## 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.

  New 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).

  New 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.

  New in version 3.5.