abstract.h (cpython/)

Include/cpython/abstract.h extends the public Include/abstract.h with declarations reserved for CPython's own C code and for embedding applications that opt into the internal ABI. The central theme is vectorcall (PEP 590): a calling convention that passes arguments as a C array instead of a Python tuple, cutting allocation overhead on every Python-to-Python and Python-to-C call.

Map

Lines	Symbol	Role
20–40	_PyObject_Vectorcall	PEP 590 core dispatcher; routes to tp_vectorcall or falls back
42–55	PyVectorcall_Call	Converts a (args, kwargs) pair into a vectorcall
57–70	_PyObject_FastCallDict	Positional array plus optional kwargs dict, no tuple
72–88	_PyObject_CallMethodIdOneArg	One-arg method call via deprecated _Py_Identifier
90–105	_PyObject_CallMethodIdObjArgs	Varargs method call via _Py_Identifier
107–120	_Py_CheckFunctionResult	Validates that a callable returned exactly one of: value or exception

Reading

Vectorcall dispatch

_PyObject_Vectorcall is the lowest-cost general call path. Callers pass a pointer to the first argument in a C array, the count encoded with the PY_VECTORCALL_ARGUMENTS_OFFSET flag, and an optional tuple of keyword names.

// CPython: Include/cpython/abstract.h:22 _PyObject_Vectorcall
static inline PyObject *
_PyObject_Vectorcall(PyObject *callable,
                     PyObject *const *args,
                     size_t nargsf,
                     PyObject *kwnames);

When callable has Py_TPFLAGS_HAVE_VECTORCALL set and tp_vectorcall_offset is non-zero, the call is dispatched through the slot with zero heap allocation. Otherwise it falls back to PyObject_Call which must build a tuple.

Converting a classic call to vectorcall

PyVectorcall_Call goes the other direction: it takes the (args_tuple, kwargs_dict) pair that PyObject_Call provides and feeds it to a vectorcall-capable callable without re-wrapping in another tuple.

// CPython: Include/cpython/abstract.h:42 PyVectorcall_Call
PyAPI_FUNC(PyObject *) PyVectorcall_Call(PyObject *callable,
                                         PyObject *tuple,
                                         PyObject *dict);

Fast-call with a keyword dict

_PyObject_FastCallDict is the bridge used by functools and inspect internals where the keyword arguments are already in a dict rather than a names-tuple.

// CPython: Include/cpython/abstract.h:57 _PyObject_FastCallDict
PyObject *
_PyObject_FastCallDict(PyObject *callable,
                       PyObject *const *args, size_t nargsf,
                       PyObject *kwargs);

Return-value validation

_Py_CheckFunctionResult enforces the invariant that every callable either returns a non-NULL object with no exception set, or returns NULL with exactly one exception set. Any other combination indicates a bug in the callable's C code.

// CPython: Include/cpython/abstract.h:107 _Py_CheckFunctionResult
PyObject *
_Py_CheckFunctionResult(PyThreadState *tstate,
                        PyObject *callable,
                        PyObject *result,
                        const char *where);

Passing a non-NULL callable causes the error message to name the callable; passing NULL uses the where string instead (useful for slot wrappers that have no Python object).

gopy notes

• _PyObject_Vectorcall is the model for vm.VectorCall in vm/eval_call.go. gopy checks tp_vectorcall_offset via the VectorcallOffset field on TypeObject.
• _Py_CheckFunctionResult has a direct equivalent in objects/protocol.go as CheckFunctionResult; the semantics match except gopy uses Go error values rather than the thread-state exception slot.
• _PyObject_CallMethodIdOneArg and _PyObject_CallMethodIdObjArgs use _Py_Identifier which is deprecated in 3.12+. gopy skips _Py_Identifier and calls method lookup directly by interned string.
• _PyObject_FastCallDict is not yet a distinct symbol in gopy; call sites use VectorCall with a manual keyword expansion.

CPython 3.14 changes

• _PyObject_CallMethodIdOneArg and _PyObject_CallMethodIdObjArgs are retained for backward compatibility but marked deprecated in 3.13 and will be removed in 3.15. New internal code uses PyObject_CallMethodOneArg instead.
• The PY_VECTORCALL_ARGUMENTS_OFFSET flag was stabilized as a public constant in 3.12; _PyObject_Vectorcall itself remains in the cpython/ tier in 3.14.
• _Py_CheckFunctionResult gained the PyThreadState parameter in 3.11 to remove the implicit _PyThreadState_GET() call from hot paths.