'Args:
ds(DataFlow): the input DataFlow.
queue (tf.QueueBase): A :class:`tf.QueueBase` whose type
should match the corresponding InputDesc of the model.
Defaults to a FIFO queue of size 50.'

def __init__(self, ds, queue=None):

    assert isinstance(ds, DataFlow), ds
    self.queue = queue
    self.ds = ds
