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.. highlight:: c
.. _typehintobjects:
Objects for Type Hinting
Various built-in types for type hinting are provided. Currently,
two types exist -- :ref:`GenericAlias <types-genericalias>` and
:ref:`Union <types-union>`. Only ``GenericAlias`` is exposed to C.
.. c:function:: PyObject* Py_GenericAlias(PyObject *origin, PyObject *args)
Create a :ref:`GenericAlias <types-genericalias>` object.
Equivalent to calling the Python class
:class:`types.GenericAlias`. The *origin* and *args* arguments set the
``GenericAlias``\ 's ``__origin__`` and ``__args__`` attributes respectively.
*origin* should be a :c:expr:`PyTypeObject*`, and *args* can be a
:c:expr:`PyTupleObject*` or any ``PyObject*``. If *args* passed is
not a tuple, a 1-tuple is automatically constructed and ``__args__`` is set
to ``(args,)``.
Minimal checking is done for the arguments, so the function will succeed even
if *origin* is not a type.
The ``GenericAlias``\ 's ``__parameters__`` attribute is constructed lazily
from ``__args__``. On failure, an exception is raised and ``NULL`` is
Here's an example of how to make an extension type generic::
static PyMethodDef my_obj_methods[] = {
// Other methods.
{"__class_getitem__", Py_GenericAlias, METH_O|METH_CLASS, "See PEP 585"}
.. seealso:: The data model method :meth:`__class_getitem__`.
.. versionadded:: 3.9
.. c:var:: PyTypeObject Py_GenericAliasType
The C type of the object returned by :c:func:`Py_GenericAlias`. Equivalent to
:class:`types.GenericAlias` in Python.
.. versionadded:: 3.9