<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_sync_model_vars_op(self):
 """ Get the op to sync local model_variables to PS. """

        ops = []
        for (shadow_v, local_v) in self._shadow_model_vars:
            ops.append(shadow_v.assign(local_v.read_value()))
        assert len(ops)
        return tf.group(*ops, name='sync_{}_model_variables_to_ps'.format(len(ops)))