def sum(self, vector):
        """Return a Vector instance as the vector sum of two vectors."""
        return self.from_list(
            [x + vector.vector[i] for i, x in self.to_list()]
        )
def sum ( self , vector ) : return self . from_list ( [ x + vector . vector [ i ] for i , x in self . to_list ( ) ] )
Return a Vector instance as the vector sum of two vectors.