transformer model based on Tensorlayer

tensorlayer/models/__init__.py

@@ -9,3 +9,4 @@
 from .vgg import *
 from .seq2seq import Seq2seq
 from .seq2seq_with_attention import Seq2seqLuongAttention
+from .transformer import *

tensorlayer/models/transformer/__init__.py

@@ -0,0 +1,6 @@
+from .attention_layer import *
+from .transformer import Transformer
+from .beamsearchHelper import *
+from .feedforward_layer import *
+from .embedding_layer import *
+from .utils import *

tensorlayer/models/transformer/attention_layer.py

@@ -0,0 +1,186 @@
+# Copyright 2018 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Implementation of multiheaded attention and self-attention layers."""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import tensorflow as tf
+import tensorlayer as tl
+
+
+class MultiHeadAttentionLayer(tl.layers.Layer):
+    """Multi-headed attention layer."""
+
+    def __init__(self, num_heads, hidden_size, keep_prob):
+        """Initialize Attention.
+
+    Args:
+      hidden_size: int, output dim of hidden layer.
+      num_heads: int, number of heads to repeat the same attention structure.
+      keep_prob: float, keep rate for dropout mechanism inside attention for training.
+    """
+        if hidden_size % num_heads:
+            raise ValueError(
+                "Hidden size ({}) must be divisible by the number of heads ({}).".format(hidden_size, num_heads)
+            )
+
+        super(MultiHeadAttentionLayer, self).__init__()
+        self.hidden_size = hidden_size
+        self.num_heads = num_heads
+        self.attention_dropout = 1 - keep_prob
+
+        self.build(None)
+        self._built = True
+
+    def get_config(self):
+        return {
+            "hidden_size": self.hidden_size,
+            "num_heads": self.num_heads,
+            "attention_dropout": self.attention_dropout,
+        }
+
+    def build(self, inputs_shape):
+        # Transformation for linearly projecting the queries, keys, and values.
+        self.q_transformation = self._get_weights(
+            "q_project", shape=(self.hidden_size, self.hidden_size), init=tf.keras.initializers.get('glorot_uniform')
+        )
+        self.v_transformation = self._get_weights(
+            "v_project", shape=(self.hidden_size, self.hidden_size), init=tf.keras.initializers.get('glorot_uniform')
+        )
+        self.k_transformation = self._get_weights(
+            "k_project", shape=(self.hidden_size, self.hidden_size), init=tf.keras.initializers.get('glorot_uniform')
+        )
+        self.out_transformation = self._get_weights(
+            "out_project", shape=(self.hidden_size, self.hidden_size), init=tf.keras.initializers.get('glorot_uniform')
+        )
+
+    def split_heads(self, x):
+        """Split x into different heads, and transpose the resulting value.
+
+    The tensor is transposed to insure the inner dimensions hold the correct
+    values during the matrix multiplication.
+
+    Args:
+      x: A tensor with shape [batch_size, length, hidden_size]
+
+    Returns:
+      A tensor with shape [batch_size, num_heads, length, hidden_size/num_heads]
+    """
+        with tf.name_scope("split_heads"):
+            batch_size = tf.shape(x)[0]
+            length = tf.shape(x)[1]
+
+            # Calculate depth of last dimension after it has been split.
+            depth = (self.hidden_size // self.num_heads)
+
+            # Split the last dimension
+            x = tf.reshape(x, [batch_size, length, self.num_heads, depth])
+
+            # Transpose the result
+            return tf.transpose(x, [0, 2, 1, 3])
+
+    def combine_heads(self, x):
+        """Combine tensor that has been split.
+
+    Args:
+      x: A tensor [batch_size, num_heads, length, hidden_size/num_heads]
+
+    Returns:
+      A tensor with shape [batch_size, length, hidden_size]
+    """
+        with tf.name_scope("combine_heads"):
+            batch_size = tf.shape(x)[0]
+            length = tf.shape(x)[2]
+            x = tf.transpose(x, [0, 2, 1, 3])  # --> [batch, length, num_heads, depth]
+            return tf.reshape(x, [batch_size, length, self.hidden_size])
+
+    def forward(self, inputs, mask, cache=None):
+        """Apply attention mechanism to x and y.
+
+    Args:
+      x: a tensor with shape [batch_size, length_x, hidden_size]
+      y: a tensor with shape [batch_size, length_y, hidden_size]
+      mask: attention bias that will be added to the result of the dot product.
+      training: boolean, whether in training mode or not.
+      cache: (Used during prediction) dictionary with tensors containing results
+        of previous attentions. The dictionary must have the items:
+            {"k": tensor with shape [batch_size, i, key_channels],
+             "v": tensor with shape [batch_size, i, value_channels]}
+        where i is the current decoded length.
+
+    Returns:
+      Attention layer output with shape [batch_size, length_x, hidden_size]
+    """
+        # Linearly project the query (q), key (k) and value (v) using different
+        # learned projections. This is in preparation of splitting them into
+        # multiple heads. Multi-head attention uses multiple queries, keys, and
+        # values rather than regular attention (which uses a single q, k, v).
+
+        if (len(inputs) == 2):
+            q = inputs[0]
+            k = v = inputs[1]
+
+        if (len(inputs) == 3):
+            q = inputs[0]
+            k = inputs[1]
+            v = inputs[2]
+
+        q = tf.tensordot(q, self.q_transformation, axes=[[2], [0]])
+        k = tf.tensordot(k, self.k_transformation, axes=[[2], [0]])
+        v = tf.tensordot(v, self.v_transformation, axes=[[2], [0]])
+
+        if cache is not None:
+
+            # Combine cached keys and values with new keys and values.
+            k = tf.concat([cache["k"], k], axis=1)
+            v = tf.concat([cache["v"], v], axis=1)
+
+            # Update cache
+            cache["k"] = k
+            cache["v"] = v
+
+        # Split q, k, v into heads.
+        q = self.split_heads(q)
+        k = self.split_heads(k)
+        v = self.split_heads(v)  #(Batch, num_head, length_v, dk)
+
+        # Scale q to prevent the dot product between q and k from growing too large.
+        depth = (self.hidden_size // self.num_heads)
+        q *= depth**-0.5
+
+        # Calculate dot product attention
+        logits = tf.matmul(q, k, transpose_b=True)  #(Batch, num_head, length_q, length_k)
+        logits += mask
+        weights = tf.nn.softmax(logits, name="attention_weights")  #(Batch, num_head, length_q, length_k)
+        if self.is_train:
+            weights = tf.nn.dropout(weights, rate=self.attention_dropout)
+
+        attention_output = tf.matmul(weights, v)
+
+        # Recombine heads --> [batch_size, length, hidden_size]
+        attention_output = self.combine_heads(attention_output)
+
+        # Run the combined outputs through another linear projection layer.
+        attention_output = tf.tensordot(attention_output, self.out_transformation, axes=[[2], [0]])
+        return attention_output
+
+
+class SelfAttentionLayer(MultiHeadAttentionLayer):
+    """Multiheaded self-attention layer."""
+
+    def forward(self, inputs, mask, cache=None):
+        return super(SelfAttentionLayer, self).forward(inputs=[inputs, inputs], mask=mask, cache=cache)

tensorlayer/models/transformer/beamsearchHelper/__init__.py

@@ -0,0 +1 @@
+from .beam_search import *

tensorlayer/models/transformer/beamsearchHelper/beam_search.py

@@ -0,0 +1,107 @@
+# Copyright 2018 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Beam search in TF v2.
+"""
+
+import tensorflow as tf
+import tensorlayer.models.transformer.beamsearchHelper.beam_search_v1 as v1
+
+_StateKeys = v1._StateKeys  # pylint: disable=protected-access
+
+
+class SequenceBeamSearchV2(v1.SequenceBeamSearch):
+    """Implementation of beam search loop in v2."""
+
+    def search(self, initial_ids, initial_cache):
+        """Beam search for sequences with highest scores."""
+        state, state_shapes = self._create_initial_state(initial_ids, initial_cache)
+        finished_state = tf.while_loop(
+            self._continue_search, self._search_step, loop_vars=[state], shape_invariants=[state_shapes],
+            parallel_iterations=1, back_prop=False
+        )
+        finished_state = finished_state[0]
+
+        alive_seq = finished_state[_StateKeys.ALIVE_SEQ]
+        alive_log_probs = finished_state[_StateKeys.ALIVE_LOG_PROBS]
+        finished_seq = finished_state[_StateKeys.FINISHED_SEQ]
+        finished_scores = finished_state[_StateKeys.FINISHED_SCORES]
+        finished_flags = finished_state[_StateKeys.FINISHED_FLAGS]
+
+        # Account for corner case where there are no finished sequences for a
+        # particular batch item. In that case, return alive sequences for that batch
+        # item.
+        finished_seq = tf.where(tf.reduce_any(finished_flags, 1), finished_seq, alive_seq)
+        finished_scores = tf.where(tf.reduce_any(finished_flags, 1), finished_scores, alive_log_probs)
+        return finished_seq, finished_scores
+
+
+def sequence_beam_search(
+        symbols_to_logits_fn, initial_ids, initial_cache, vocab_size, beam_size, alpha, max_decode_length, eos_id
+):
+    """Search for sequence of subtoken ids with the largest probability.
+
+    Args:
+        symbols_to_logits_fn: A function that takes in ids, index, and cache as
+        arguments. The passed in arguments will have shape:
+            ids -> [batch_size * beam_size, index]
+            index -> [] (scalar)
+            cache -> nested dictionary of tensors [batch_size * beam_size, ...]
+        The function must return logits and new cache.
+            logits -> [batch * beam_size, vocab_size]
+            new cache -> same shape/structure as inputted cache
+        initial_ids: Starting ids for each batch item.
+        int32 tensor with shape [batch_size]
+        initial_cache: dict containing starting decoder variables information
+        vocab_size: int size of tokens
+        beam_size: int number of beams
+        alpha: float defining the strength of length normalization
+        max_decode_length: maximum length to decoded sequence
+        eos_id: int id of eos token, used to determine when a sequence has finished
+
+    Returns:
+        Top decoded sequences [batch_size, beam_size, max_decode_length]
+        sequence scores [batch_size, beam_size]
+    """
+    batch_size = tf.shape(initial_ids)[0]
+
+    sbs = SequenceBeamSearchV2(
+        symbols_to_logits_fn, vocab_size, batch_size, beam_size, alpha, max_decode_length, eos_id
+    )
+    return sbs.search(initial_ids, initial_cache)
+
+
+def _expand_to_same_rank(tensor, target):
+    """Expands a given tensor to target's rank to be broadcastable.
+
+    Args:
+        tensor: input tensor to tile. Shape: [b, d1, ..., da]
+        target: target tensor. Shape: [b, d1, ..., da, ..., dn]
+
+    Returns:
+        Tiled tensor of shape [b, d1, ..., da, 1, ..., 1] with same rank of target.
+
+    Raises:
+        ValueError, if the shape rank of rank tensor/target is None.
+    """
+    if tensor.shape.rank is None:
+        raise ValueError("Expect rank for tensor shape, but got None.")
+    if target.shape.rank is None:
+        raise ValueError("Expect rank for target shape, but got None.")
+
+    with tf.name_scope("expand_rank"):
+        diff_rank = target.shape.rank - tensor.shape.rank
+        for _ in range(diff_rank):
+            tensor = tf.expand_dims(tensor, -1)
+        return tensor