code: def _fit_islands(self, islands):
          
          self.log.debug("Fitting group of {0} islands".format(len(islands)))
          sources = []
          for island in islands:
              res = self._fit_island(island)
              sources.extend(res)
          return sources
docs: Execute fitting on a list of islands
          This function just wraps around fit_island, so that when we do multiprocesing
          a single process will fit multiple islands before returning results.
  
  
          Parameters
          ----------
          islands : list of :class:`AegeanTools.models.IslandFittingData`
              The islands to be fit.
  
          Returns
          -------
          sources : list
              The sources that were fit.