<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def faces(self, values):
 """ Set the vertex indexes that make up triangular faces. Parameters values : (n, 3) int Indexes of self.vertices """

        if values is None:
            values = []
        values = np.asanyarray(values, dtype=np.int64)
        # automatically triangulate quad faces
        if util.is_shape(values, (-1, 4)):
            log.info('triangulating quad faces')
            values = geometry.triangulate_quads(values)
        self._data['faces'] = values