Read/write boolean specifying whether number formatting should be
        taken from the source spreadsheet rather than the value of
        :meth:`number_format`.

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