def __init__ (self, id_gen = 'max') :
     """Constructor of an empty mesh
     
     :Parameters:
      - `idgenerator` (str) - type of id gen used in the
                              mesh
     """
     Topomesh.__init__(self, id_gen)
     
     self._pos = {}
 def remove_dart (self, did) :
     Topomesh.remove_dart(self, did)
     self._pos.pop(did, None)
 def add_dart (self, degree, did = None) :
     did = Topomesh.add_dart(self, degree, did)
     if degree == 0 :
         self._pos[did] = None
     
     return did
 def clear (self) :
     Topomesh.clear(self)
     self._pos.clear()