code: def rewrite_guides(self, guides):
          
          self._remove_avLst()
          avLst = self._add_avLst()
          for name, val in guides:
              gd = avLst._add_gd()
              gd.name = name
              gd.fmla = 'val %d' % val
docs: Remove any ``<a:gd>`` element children of ``<a:avLst>`` and replace
          them with ones having (name, val) in *guides*.