code: def _AddHasExtensionMethod(cls):
    
    def HasExtension(self, extension_handle):
      _VerifyExtensionHandle(self, extension_handle)
      if extension_handle.label == _FieldDescriptor.LABEL_REPEATED:
        raise KeyError('"%s" is repeated.' % extension_handle.full_name)
  
      if extension_handle.cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
        value = self._fields.get(extension_handle)
        return value is not None and value._is_present_in_parent
      else:
        return extension_handle in self._fields
    cls.HasExtension = HasExtension
docs: Helper for _AddMessageMethods().