code: def add_extension(module, name, code):
      
      code = int(code)
      if not 1 <= code <= 0x7fffffff:
          raise ValueError, "code out of range"
      key = (module, name)
      if (_extension_registry.get(key) == code and
          _inverted_registry.get(code) == key):
          return # Redundant registrations are benign
      if key in _extension_registry:
          raise ValueError("key %s is already registered with code %s" %
                           (key, _extension_registry[key]))
      if code in _inverted_registry:
          raise ValueError("code %s is already in use for key %s" %
                           (code, _inverted_registry[code]))
      _extension_registry[key] = code
      _inverted_registry[code] = key
docs: Register an extension code.