code: def _val_pt_xml(self):
          
          xml = ''
          for idx, value in enumerate(self._series.values):
              if value is None:
                  continue
              xml += (
                  '                <c:pt idx="{val_idx:d}">\n'
                  '                  <c:v>{value}</c:v>\n'
                  '                </c:pt>\n'
              ).format(**{
                  'val_idx': idx,
                  'value':   value,
              })
          return xml
docs: The unicode XML snippet containing the ``<c:pt>`` elements containing
          the values for this series.