cpython/Include/cpython/tupleobject.h

#ifndef Py_CPYTHON_TUPLEOBJECT_H
#  error "this header file must not be included directly"
#endif

PyTupleObject;

PyAPI_FUNC(int) _PyTuple_Resize(PyObject **, Py_ssize_t);

/* Cast argument to PyTupleObject* type. */
#define _PyTuple_CAST(op) …

// Macros and static inline functions, trading safety for speed

static inline Py_ssize_t PyTuple_GET_SIZE(PyObject *op) { … }
#define PyTuple_GET_SIZE(op) …

#define PyTuple_GET_ITEM(op, index) …

/* Function *only* to be used to fill in brand new tuples */
static inline void
PyTuple_SET_ITEM(PyObject *op, Py_ssize_t index, PyObject *value) { … }
#define PyTuple_SET_ITEM(op, index, value) …