Use _PyUnicodeWriter API in str.format() internals

Include/longobject.h

 #ifndef Py_LONGOBJECT_H
 #define Py_LONGOBJECT_H
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 
 /* Long (arbitrary precision) integer object interface */
 
 typedef struct _longobject PyLongObject; /* Revealed in longintrepr.h */
@@ skipping 136 matching lines @@
 PyAPI_FUNC(int) _PyLong_AsByteArray(PyLongObject* v,
     unsigned char* bytes, size_t n,
     int little_endian, int is_signed);
 
 
 /* _PyLong_Format: Convert the long to a string object with given base,
    appending a base prefix of 0[box] if base is 2, 8 or 16. */
 PyAPI_FUNC(PyObject *) _PyLong_Format(PyObject *aa, int base);
 
 /* Format the object based on the format_spec, as defined in PEP 3101
-   (Advanced String Formatting). */
-PyAPI_FUNC(PyObject *) _PyLong_FormatAdvanced(PyObject *obj,
-                                              PyObject *format_spec,
-                                              Py_ssize_t start,
-                                              Py_ssize_t end);
+   (Advanced String Formatting). Return 0 on success, raise an exception
+   and return -1 on error. */
+PyAPI_FUNC(int) _PyLong_FormatWriter(PyObject *obj,
+                                     PyObject *format_spec,
+                                     Py_ssize_t start,
+                                     Py_ssize_t end,
+                                     _PyUnicodeWriter *writer);
 #endif /* Py_LIMITED_API */
 
 /* These aren't really part of the long object, but they're handy. The
    functions are in Python/mystrtoul.c.
  */
 PyAPI_FUNC(unsigned long) PyOS_strtoul(char *, char **, int);
 PyAPI_FUNC(long) PyOS_strtol(char *, char **, int);
 
 #ifdef __cplusplus
 }
 #endif
 #endif /* !Py_LONGOBJECT_H */