code: def flat_map(self, flatmap_function):
      
      from heronpy.streamlet.impl.flatmapbolt import FlatMapStreamlet
      fm_streamlet = FlatMapStreamlet(flatmap_function, self)
      self._add_child(fm_streamlet)
      return fm_streamlet
docs: Return a new Streamlet by applying map_function to each element of this Streamlet
         and flattening the result