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

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.

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

Dynamic Type Creation¶

Standard Interpreter Types¶

Additional Utility Classes and Functions¶

Coroutine Utility Functions¶

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types — Dynamic type creation and names for built-in types¶

Dynamic Type Creation¶

Standard Interpreter Types¶

Additional Utility Classes and Functions¶

Coroutine Utility Functions¶

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