code: def number_format_is_linked(self):
          
          numFmt = self._element.numFmt
          if numFmt is None:
              return True
          souceLinked = numFmt.sourceLinked
          if souceLinked is None:
              return True
          return numFmt.sourceLinked
docs: Read/write boolean specifying whether number formatting should be
          taken from the source spreadsheet rather than the value of
          :meth:`number_format`.