code: def calling_convention(self):
          
          if self._calling_convention is None:
              self._calling_convention = \
                  calldef_types.CALLING_CONVENTION_TYPES.extract(self.attributes)
              if not self._calling_convention:
                  self._calling_convention = self.guess_calling_convention()
          return self._calling_convention
docs: function calling convention. See
              :class:CALLING_CONVENTION_TYPES class for possible values