tf.contrib.seq2seq.Decoder

Class Decoder

Defined in tensorflow/contrib/seq2seq/python/ops/decoder.py.

See the guide: Seq2seq Library (contrib) > Dynamic Decoding

An RNN Decoder abstract interface object.

Concepts used by this interface: - inputs: (structure of) tensors and TensorArrays that is passed as input to the RNNCell composing the decoder, at each time step. - state: (structure of) tensors and TensorArrays that is passed to the RNNCell instance as the state. - finished: boolean tensor telling whether each sequence in the batch is finished. - outputs: Instance of BasicDecoderOutput. Result of the decoding, at each time step.

Properties

batch_size

The batch size of input values.

output_dtype

A (possibly nested tuple of...) dtype[s].

output_size

A (possibly nested tuple of...) integer[s] or TensorShape object[s].

tracks_own_finished

Describes whether the Decoder keeps track of finished states.

Most decoders will emit a true/false finished value independently at each time step. In this case, the dynamic_decode function keeps track of which batch entries are already finished, and performs a logical OR to insert new batches to the finished set.

Some decoders, however, shuffle batches / beams between time steps and dynamic_decode will mix up the finished state across these entries because it does not track the reshuffle across time steps. In this case, it is up to the decoder to declare that it will keep track of its own finished state by setting this property to True.

Returns:

Python bool.

Methods

finalize

finalize(
    outputs,
    final_state,
    sequence_lengths
)

initialize

initialize(name=None)

Called before any decoding iterations.

This methods must compute initial input values and initial state.

Args:

• name: Name scope for any created operations.

Returns:

(finished, initial_inputs, initial_state): initial values of 'finished' flags, inputs and state.

step

step(
    time,
    inputs,
    state,
    name=None
)

Called per step of decoding (but only once for dynamic decoding).

Args:

• time: Scalar int32 tensor. Current step number.
• inputs: RNNCell input (possibly nested tuple of) tensor[s] for this time step.
• state: RNNCell state (possibly nested tuple of) tensor[s] from previous time step.
• name: Name scope for any created operations.

Returns:

(outputs, next_state, next_inputs, finished): outputs is an object containing the decoder output, next_state is a (structure of) state tensors and TensorArrays, next_inputs is the tensor that should be used as input for the next step, finished is a boolean tensor telling whether the sequence is complete, for each sequence in the batch.