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Include/internal/pycore_atexit.h

Source:

cpython 3.14 @ ab2d84fe1023/Include/internal/pycore_atexit.h

pycore_atexit.h declares the per-interpreter atexit callback state. atexit.register appends to this list; Py_FinalizeEx drains it in LIFO order.

Map​

LinesSymbolRole
1-30atexit_callbackA single registered callback: callable + args + kwargs
31-50_PyAtExit_StateList of callbacks embedded in PyInterpreterState
51-60_Py_AtExitC-level registration (used by Py_AtExit)

Reading​

atexit_callback​

// CPython: Include/internal/pycore_atexit.h:14 atexit_callback
typedef struct {
    PyObject *func;
    PyObject *args;
    PyObject *kwargs;
} atexit_callback;

_PyAtExit_State​

// CPython: Include/internal/pycore_atexit.h:22 _PyAtExit_State
struct _PyAtExit_State {
    atexit_callback **callbacks;  /* dynamically grown array */
    int ncallbacks;               /* number of registered callbacks */
    int callback_len;             /* allocated capacity */
};

How atexit.register uses this​

# CPython: Lib/atexit.py (backed by Modules/atexitmodule.c)
# atexit.register(func, *args, **kwargs) appends to callbacks[]
# Py_FinalizeEx calls _PyAtExit_Call() which iterates in reverse:
# for i in range(ncallbacks-1, -1, -1):
#     callbacks[i].func(*callbacks[i].args, **callbacks[i].kwargs)

Callbacks are called in LIFO (last-in, first-out) order. Exceptions in callbacks are printed to sys.stderr but do not stop the remaining callbacks.

_Py_AtExit (C-level)​

// CPython: Include/internal/pycore_atexit.h:52 _Py_AtExit
/* Register a C function to be called at interpreter shutdown.
   Used internally (e.g. by readline cleanup). */
int _Py_AtExit(PyInterpreterState *interp,
               atexit_datacallbackfunc func,
               void *data);

This C-level API registers a (func, data) pair and is separate from the Python atexit module's callback list.

gopy notes​

gopy stores atexit state in vm/atexit.go as a []atexitEntry on the interpreter. atexit.register appends via module/atexit/module.go. vm.RunAtExit() is called from Py_FinalizeEx in LIFO order. C-level _Py_AtExit is not exposed since gopy has no C extension ABI.