The limited C API is now supported if Python is built in debug mode
(if the Py_DEBUG macro is defined). In the limited C API, the
Py_INCREF() and Py_DECREF() functions are now implemented as opaque
function calls, rather than accessing directly the PyObject.ob_refcnt
member, if Python is built in debug mode and the Py_LIMITED_API macro
targets Python 3.10 or newer. It became possible to support the
limited C API in debug mode because the PyObject structure is the
same in release and debug mode since Python 3.8 (see bpo-36465).
The limited C API is still not supported in the --with-trace-refs
special build (Py_TRACE_REFS macro).
The Python C API
================
The C API is divided into three sections:
1. ``Include/``
2. ``Include/cpython/``
3. ``Include/internal/``
Include: Limited API
====================
``Include/``, excluding the ``cpython`` and ``internal`` subdirectories,
contains the public Limited API (Application Programming Interface).
The Limited API is a subset of the C API, designed to guarantee ABI
stability across Python 3 versions, and is defined in :pep:`384`.
Guidelines for expanding the Limited API:
- Functions *must not* steal references
- Functions *must not* return borrowed references
- Functions returning references *must* return a strong reference
- Macros should not expose implementation details
- Please start a public discussion before expanding the API
- Functions or macros with a ``_Py`` prefix do not belong in ``Include/``.
It is possible to add a function or macro to the Limited API from a
given Python version. For example, to add a function to the Limited API
from Python 3.10 and onwards, wrap it with
``#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030A0000``.
Include/cpython: CPython implementation details
===============================================
``Include/cpython/`` contains the public API that is excluded from the
Limited API and the Stable ABI.
Guidelines for expanding the public API:
- Functions *must not* steal references
- Functions *must not* return borrowed references
- Functions returning references *must* return a strong reference
Include/internal: The internal API
==================================
With PyAPI_FUNC or PyAPI_DATA
-----------------------------
Functions or structures in ``Include/internal/`` defined with
``PyAPI_FUNC`` or ``PyAPI_DATA`` are internal functions which are
exposed only for specific use cases like debuggers and profilers.
With the extern keyword
-----------------------
Functions in ``Include/internal/`` defined with the ``extern`` keyword
*must not and can not* be used outside the CPython code base. Only
built-in stdlib extensions (built with the ``Py_BUILD_CORE_BUILTIN``
macro defined) can use such functions.
When in doubt, new internal C functions should be defined in
``Include/internal`` using the ``extern`` keyword.
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