cpython/Modules/_testlimitedcapi/util.h

#define NULLABLE(x) …

#define RETURN_INT(value) …

#define RETURN_SIZE(value) …

/* Marker to check that pointer value was set. */
static const char uninitialized[] = …;
#define UNINITIALIZED_PTR …
/* Marker to check that Py_ssize_t value was set. */
#define UNINITIALIZED_SIZE …
/* Marker to check that integer value was set. */
#define UNINITIALIZED_INT …