Both functions raise an exception if `obj` does not support the relevant protocol.

METH_FASTCALL and METH_VECTORCALL flags

A new ``METH_VECTORCALL`` flag is added for specifying ``MethodDef`` structs. It is equivalent to the currently undocumented ``METH_FASTCALL | METH_KEYWORD`` flag.

The new flag specifies that the function has the type ``PyObject *(*call) (PyObject * self, PyObject *const *args, Py_ssize_t nargs, PyObject *kwname)``

or proxies.

Other rejected approaches

A longer, 6 argument, form combining both the vector and optional tuple and dictionary arguments was considered.

However, it was found that the code to convert between it and the old `tp_call` form was overly cumbersome and inefficient.

then it would be too slow.

Acknowledgements

Victor Stinner for developing the original "vector call" calling convention internally to CPython (where is it is called "fast call")

this PEP codifies and extends his work.

Jeroen Demeyer for authoring PEP 575 and PEP 580 which helped motivate this PEP.

References

.. [1]Calling conventions