Objects for Type Hinting

.. highlight:: c

.. _typehintobjects:

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 returned.

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:~object.__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