# Objects for Type Hinting

Various built-in types for type hinting are provided. Currently, two types exist – GenericAlias and Union. Only `GenericAlias` is exposed to C.

PyObject *`Py_GenericAlias`(PyObject *origin, PyObject *args)
  Part of the Stable ABI since version 3.9.

  Create a GenericAlias object. Equivalent to calling the Python class `types.GenericAlias`. The origin and args arguments set the `GenericAlias`‘s `__origin__` and `__args__` attributes respectively. origin should be a PyTypeObject*, and args can be a 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__", (PyCFunction)Py_GenericAlias, METH_O|METH_CLASS, "See PEP 585"}
          ...
      }

  See also

  The data model method `__class_getitem__()`.

  New in version 3.9.

PyTypeObject `Py_GenericAliasType`
  Part of the Stable ABI since version 3.9.

  The C type of the object returned by `Py_GenericAlias()`. Equivalent to `types.GenericAlias` in Python.

  New in version 3.9.