The "current" or "old" C API is the Python 3.7 API which "leaks" implementation details like PyObject.ob_refcnt through :ref:`Py_INCREF() <incref>` macro.

With the new C API, the old C API will remain available thanks to the :ref:`regular runtime <regular-runtime>`, for CPython internals, for specific use cases like :ref:`Cython <cython>` (for best performances) and :ref:`debugging tools <debug-tools>`, but also for the long tail of C extensions on PyPI.

See also :ref:`Calling conventions <calling-conventions>`.

• Python objects
  • Protocol, Abstract
  • Types, Classes
• Memory Allocators
• Python initialization and configuration
• Control flow
  • Generator
  • Exception: PyErr_SetString(), PyErr_Clear()

• CPython: headers of the Include/ directory
• PyPy :ref:`cpyext <cpyext>`: pypy/module/cpyext/ (cpyext/stubs.py)