Add GPT-2 Model and its Variants

keras_nlp/models/__init__.py

@@ -19,6 +19,11 @@
 from keras_nlp.models.bert import BertMedium
 from keras_nlp.models.bert import BertSmall
 from keras_nlp.models.bert import BertTiny
+from keras_nlp.models.gpt2 import Gpt2Base
+from keras_nlp.models.gpt2 import Gpt2Custom
+from keras_nlp.models.gpt2 import Gpt2ExtraLarge
+from keras_nlp.models.gpt2 import Gpt2Large
+from keras_nlp.models.gpt2 import Gpt2Medium
 from keras_nlp.models.roberta import RobertaBase
 from keras_nlp.models.roberta import RobertaClassifier
 from keras_nlp.models.roberta import RobertaCustom

keras_nlp/models/bert.py

@@ -144,8 +144,8 @@ class BertCustom(keras.Model):
     or classification task networks.
 
     This class gives a fully customizable BERT model with any number of layers,
-    heads, and embedding dimensions. For specific specific bert architectures
-    defined in the paper, see for example `keras_nlp.models.BertBase`.
+    heads, and embedding dimensions. For specific BERT architectures
+    defined in the paper, see, for example, `keras_nlp.models.BertBase`.
 
     Args:
         vocabulary_size: Int. The size of the token vocabulary.
@@ -405,7 +405,7 @@ def __init__(
             If None, model is randomly initialized. Either `weights` or
             `vocabulary_size` must be specified, but not both.
         vocabulary_size: Int, optional. The size of the token vocabulary. Either
-            `weights` or `vocabularly_size` must be specified, but not both.
+            `weights` or `vocabulary_size` must be specified, but not both.
         name: String, optional. Name of the model.
         trainable: Boolean, optional. If the model's variables should be
             trainable.

keras_nlp/models/gpt2.py

@@ -0,0 +1,287 @@
+# Copyright 2022 The KerasNLP Authors
+#
+# 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
+#
+#     https://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.
+
+"""GPT-2 model configurable class, preconfigured versions, and task heads."""
+
+import tensorflow as tf
+from tensorflow import keras
+
+from keras_nlp.layers import PositionEmbedding
+from keras_nlp.layers import TransformerDecoder
+
+
+def _gpt_2_kernel_initializer(stddev=0.02):
+    return keras.initializers.RandomNormal(stddev=stddev)
+
+
+class Gpt2Custom(keras.Model):
+    """Generative Pretrained Transformer-2 (GPT-2) network.
+
+    This network implements a Transformer-based decoder as
+    described in
+    ["Language Models are Unsupervised Multitask Learners"](https://cdn.openai.com/better-language-models/language_models_are_unsupervised_multitask_learners.pdf).
+    It includes the embedding lookups and transformer layers, but not the
+    language modeling or classification task heads.
+
+    This class gives a fully customizable GPT-2 model with any number of layers,
+    heads, and embedding dimensions. For specific GPT-2 architectures
+    defined in the paper, see, for example, `keras_nlp.models.Gpt2Base`.
+
+    Args:
+        vocabulary_size: int. The size of the token vocabulary.
+        num_layers: int. The number of transformer layers.
+        num_heads: int. The number of attention heads for each transformer.
+            The hidden size must be divisible by the number of attention heads.
+        hidden_dim: int. The size of the transformer encoding and pooler layers.
+        intermediate_dim: int. The output dimension of the first Dense layer in
+            a two-layer feedforward network for each transformer.
+        dropout: float. Dropout probability for the Transformer encoder.
+        max_sequence_length: int. The maximum sequence length that this encoder
+            can consume. If None, `max_sequence_length` uses the value from
+            sequence length. This determines the variable shape for positional
+            embeddings.
+        name: string, optional. Name of the model.
+        trainable: boolean, optional. If the model's variables should be
+            trainable.
+
+    Example usage:
+    ```python
+    # Randomly initialized GPT-2 decoder
+    model = keras_nlp.models.Gpt2Custom(
+        vocabulary_size=50257,
+        num_layers=12,
+        num_heads=12,
+        hidden_dim=768,
+        intermediate_dim=3072,
+        max_sequence_length=1024,
+        name="encoder",
+    )
+
+    # Call encoder on the inputs
+    input_data = {
+        "token_ids": tf.random.uniform(
+            shape=(1, 12), dtype=tf.int64, maxval=model.vocabulary_size
+        ),
+        "padding_mask": tf.constant(
+            [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0], shape=(1, 12)
+        ),
+    }
+    output = model(input_data)
+    ```
+    """
+
+    def __init__(
+        self,
+        vocabulary_size,
+        num_layers,
+        num_heads,
+        hidden_dim,
+        intermediate_dim,
+        dropout=0.1,
+        max_sequence_length=1024,
+        name=None,
+        trainable=True,
+    ):
+
+        # Inputs
+        token_ids = keras.Input(shape=(None,), dtype="int32", name="token_ids")
+        padding_mask = keras.Input(
+            shape=(None,), dtype="int32", name="padding_mask"
+        )
+
+        # Embed tokens, positions.
+        token_embedding = keras.layers.Embedding(
+            input_dim=vocabulary_size,
+            output_dim=hidden_dim,
+            embeddings_initializer=_gpt_2_kernel_initializer(stddev=0.01),
+            name="token_embedding",
+        )(token_ids)
+
+        position_embedding = PositionEmbedding(
+            initializer=_gpt_2_kernel_initializer(stddev=0.02),
+            sequence_length=max_sequence_length,
+            name="position_embedding",
+        )(token_embedding)
+
+        # Sum and apply dropout to embeddings.
+        x = keras.layers.Add()((token_embedding, position_embedding))
+        x = keras.layers.Dropout(
+            dropout,
+            name="embeddings_dropout",
+        )(x)
+
+        # Apply successive transformer decoder blocks.
+        for i in range(num_layers):
+            x = TransformerDecoder(
+                intermediate_dim=intermediate_dim,
+                num_heads=num_heads,
+                dropout=dropout,
+                activation=lambda x: keras.activations.gelu(
+                    x, approximate=True
+                ),
+                layer_norm_epsilon=1e-05,
+                kernel_initializer=_gpt_2_kernel_initializer(stddev=0.02),
+                normalize_first=True,
+                name=f"transformer_layer_{i}",
+            )(x, decoder_padding_mask=padding_mask)
+
+        sequence_output = keras.layers.LayerNormalization(
+            name="layer_norm",
+            axis=-1,
+            epsilon=1e-05,
+            dtype=tf.float32,
+        )(x)
+
+        # Instantiate using Functional API Model constructor
+        super().__init__(
+            inputs={
+                "token_ids": token_ids,
+                "padding_mask": padding_mask,
+            },
+            outputs=sequence_output,
+            name=name,
+            trainable=trainable,
+        )
+        # All references to `self` below this line
+        self.vocabulary_size = vocabulary_size
+        self.num_layers = num_layers
+        self.num_heads = num_heads
+        self.hidden_dim = hidden_dim
+        self.intermediate_dim = intermediate_dim
+        self.dropout = dropout
+        self.max_sequence_length = max_sequence_length
+
+    def get_config(self):
+        config = super().get_config()
+        config.update(
+            {
+                "vocabulary_size": self.vocabulary_size,
+                "num_layers": self.num_layers,
+                "num_heads": self.num_heads,
+                "hidden_dim": self.hidden_dim,
+                "intermediate_dim": self.intermediate_dim,
+                "dropout": self.dropout,
+                "max_sequence_length": self.max_sequence_length,
+            }
+        )
+        return config
+
+
+MODEL_DOCSTRING = """GPT-2 implementation using "{type}"
+    architecture (with {num_params} parameters).
+
+    This network implements a Transformer-based decoder as
+    described in
+    ["Language Models are Unsupervised Multitask Learners"](https://cdn.openai.com/better-language-models/language_models_are_unsupervised_multitask_learners.pdf).
+    It includes the embedding lookups and transformer layers, but not the
+    language modeling or classification task heads.
+
+    Args:
+        vocabulary_size: int, optional. The size of the token vocabulary.
+        name: String, optional. Name of the model.
+        trainable: boolean, optional. If the model's variables should be
+            trainable.
+
+    Example usage:
+    ```python
+    # Randomly initialized Gpt2{type} encoder
+    model = keras_nlp.models.Gpt2{type}(vocabulary_size=10000)
+
+    # Call encoder on the inputs.
+    input_data = {{
+        "token_ids": tf.random.uniform(
+            shape=(1, 1024), dtype=tf.int64, maxval=model.vocabulary_size
+        ),
+        "padding_mask": tf.constant([1] * 1024, shape=(1, 1024)),
+    }}
+    output = model(input_data)
+"""
+
+
+def Gpt2Base(vocabulary_size, name=None, trainable=True):
+    return Gpt2Custom(
+        vocabulary_size=vocabulary_size,
+        num_layers=12,
+        num_heads=12,
+        hidden_dim=768,
+        intermediate_dim=3072,
+        dropout=0.1,
+        max_sequence_length=1024,
+        name=name,
+        trainable=trainable,
+    )
+
+
+def Gpt2Medium(vocabulary_size, name=None, trainable=True):
+    return Gpt2Custom(
+        vocabulary_size=vocabulary_size,
+        num_layers=24,
+        num_heads=16,
+        hidden_dim=1024,
+        intermediate_dim=4096,
+        dropout=0.1,
+        max_sequence_length=1024,
+        name=name,
+        trainable=trainable,
+    )
+
+
+def Gpt2Large(vocabulary_size, name=None, trainable=True):
+    return Gpt2Custom(
+        vocabulary_size=vocabulary_size,
+        num_layers=36,
+        num_heads=20,
+        hidden_dim=1280,
+        intermediate_dim=5120,
+        dropout=0.1,
+        max_sequence_length=1024,
+        name=name,
+        trainable=trainable,
+    )
+
+
+def Gpt2ExtraLarge(vocabulary_size, name=None, trainable=True):
+    return Gpt2Custom(
+        vocabulary_size=vocabulary_size,
+        num_layers=48,
+        num_heads=25,
+        hidden_dim=1600,
+        intermediate_dim=6400,
+        dropout=0.1,
+        max_sequence_length=1024,
+        name=name,
+        trainable=trainable,
+    )
+
+
+setattr(
+    Gpt2Base,
+    "__doc__",
+    MODEL_DOCSTRING.format(type="Base", num_params="124M"),
+)
+setattr(
+    Gpt2Medium,
+    "__doc__",
+    MODEL_DOCSTRING.format(type="Medium", num_params="355M"),
+)
+setattr(
+    Gpt2Large,
+    "__doc__",
+    MODEL_DOCSTRING.format(type="Large", num_params="774M"),
+)
+setattr(
+    Gpt2ExtraLarge,
+    "__doc__",
+    MODEL_DOCSTRING.format(type="ExtraLarge", num_params="1558M"),
+)