code: def md5(self):
          
          # first MD5 the points in every entity
          target = '{}{}'.format(
              util.md5_object(bytes().join(e._bytes()
                                           for e in self.entities)),
              self.vertices.md5())
  
          return target
docs: An MD5 hash of the current vertices and entities.
  
          Returns
          ------------
          md5: str, two appended MD5 hashes