'Device used to create the clone and all the ops inside the clone.
Args:
clone_index: Int, representing the clone_index.
Returns:
A value suitable for `tf.device()`.
Raises:
ValueError: if `clone_index` is greater or equal to the number of clones".'

def clone_device(self, clone_index):

    if (clone_index >= self._num_clones):
        raise ValueError('clone_index    must    be    less    than    num_clones')
    device = ''
    if (self._num_ps_tasks > 0):
        device += self._worker_device
    if self._clone_on_cpu:
        device += '/device:CPU:0'
    elif (self._num_clones > 1):
        device += ('/device:GPU:%d' % clone_index)
    return device
