Add GPT2 text generation stuff

keras_nlp/models/__init__.py

@@ -26,6 +26,11 @@
 from keras_nlp.models.distil_bert.distil_bert_tokenizer import (
     DistilBertTokenizer,
 )
+from keras_nlp.models.gpt2.gpt2_backbone import GPT2Backbone
+from keras_nlp.models.gpt2.gpt2_causal_lm import GPT2CausalLM
+from keras_nlp.models.gpt2.gpt2_preprocessor import GPT2CausalLMPreprocessor
+from keras_nlp.models.gpt2.gpt2_preprocessor import GPT2Preprocessor
+from keras_nlp.models.gpt2.gpt2_tokenizer import GPT2Tokenizer
 from keras_nlp.models.roberta.roberta_backbone import RobertaBackbone
 from keras_nlp.models.roberta.roberta_classifier import RobertaClassifier
 from keras_nlp.models.roberta.roberta_preprocessor import RobertaPreprocessor

keras_nlp/models/gpt2/gpt2_causal_lm.py

@@ -0,0 +1,110 @@
+# 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.
+"""BERT task specific models and heads."""
+
+import copy
+
+import tensorflow as tf
+from tensorflow import keras
+
+from keras_nlp.models.gpt2.gpt2_backbone import GPT2Backbone
+from keras_nlp.models.gpt2.gpt2_preprocessor import GPT2CausalLMPreprocessor
+from keras_nlp.models.gpt2.gpt2_presets import backbone_presets
+from keras_nlp.samplers.beam_sampler import BeamSampler
+from keras_nlp.samplers.greedy_sampler import GreedySampler
+from keras_nlp.samplers.top_k_sampler import TopKSampler
+from keras_nlp.samplers.top_p_sampler import TopPSampler
+from keras_nlp.utils.pipeline_model import PipelineModel
+from keras_nlp.utils.python_utils import classproperty
+
+
+@keras.utils.register_keras_serializable(package="keras_nlp")
+class GPT2CausalLM(PipelineModel):
+    def __init__(self, backbone, preprocessor=None, **kwargs):
+
+        inputs = backbone.input
+        x = backbone(inputs)
+        x = tf.matmul(
+            x,
+            backbone.get_layer("token_embedding").embeddings,
+            transpose_b=True,
+        )
+        outputs = tf.keras.layers.Softmax()(x)
+        # Instantiate using Functional API Model constructor
+        super().__init__(
+            inputs=inputs,
+            outputs=outputs,
+            include_preprocessing=preprocessor is not None,
+            **kwargs,
+        )
+
+        self.preprocessor = preprocessor
+        self.backbone = backbone
+
+    def preprocess_samples(self, x, y=None, sample_weight=None):
+        return self.preprocessor(x, y=y, sample_weight=sample_weight)
+
+    @classproperty
+    def presets(cls):
+        return copy.deepcopy(backbone_presets)
+
+    @classmethod
+    def from_preset(
+        cls,
+        preset,
+        load_weights=True,
+        **kwargs,
+    ):
+        if "preprocessor" not in kwargs:
+            kwargs["preprocessor"] = GPT2CausalLMPreprocessor.from_preset(
+                preset
+            )
+
+        # Check if preset is backbone-only model.
+        if preset in GPT2Backbone.presets:
+            backbone = GPT2Backbone.from_preset(preset, load_weights)
+            return cls(backbone, **kwargs)
+
+        # Otherwise must be one of class presets.
+        # Currently no classifier-level presets, so we raise ValueError.
+        if preset not in cls.presets:
+            raise ValueError(
+                "`preset` must be one of "
+                f"""{", ".join(cls.presets)}. Received: {preset}."""
+            )
+
+    def _get_generator(self, identifier):
+        maps = {
+            "greedy": GreedySampler(),
+            "top_k": TopKSampler(k=5, from_logits=False),
+            "top_p": TopPSampler(p=0.1, from_logits=False),
+            "beam": BeamSampler(num_beams=5),
+        }
+        return maps[identifier]
+
+    def _get_token_probability(self, prompt, mask):
+        model_inputs = {
+            "token_ids": prompt,
+            "padding_mask": mask,
+        }
+        probs = self(model_inputs)
+        return probs
+
+    def generate(self, prompt, max_length, generator="top_k"):
+        """Pick one method as the default generation algo."""
+        if isinstance(generator, str):
+            generator = self._get_generator(generator)
+        prompt = self.preprocessor.tokenizer(prompt)
+        generated = generator(self._get_token_probability, prompt, max_length)
+        return self.preprocessor.tokenizer.detokenize(generated)

keras_nlp/models/gpt2/gpt2_preprocessor.py

@@ -0,0 +1,102 @@
+# 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.
+
+"""GPT2 preprocessor layer."""
+
+import copy
+
+import tensorflow as tf
+from tensorflow import keras
+
+from keras_nlp.models.gpt2.gpt2_presets import backbone_presets
+from keras_nlp.models.gpt2.gpt2_tokenizer import GPT2Tokenizer
+from keras_nlp.utils.keras_utils import pack_x_y_sample_weight
+from keras_nlp.utils.python_utils import classproperty
+
+
+class GPT2Preprocessor(keras.layers.Layer):
+    def __init__(self, tokenizer, sequence_length, **kwargs):
+
+        super().__init__(**kwargs)
+
+        self.tokenizer = tokenizer
+        self.sequence_length = sequence_length
+
+    def call(self, x, y=None, sample_weight=None):
+        token_ids = self.tokenizer(x)
+        mask = tf.ones_like(token_ids, dtype=tf.bool)
+        mask = mask.to_tensor(shape=(None, self.sequence_length))
+        token_ids = token_ids.to_tensor(shape=(None, self.sequence_length))
+        x = {
+            "token_ids": token_ids,
+            "padding_mask": mask,
+        }
+
+        return pack_x_y_sample_weight(x, y, sample_weight)
+
+    @classproperty
+    def presets(cls):
+        return copy.deepcopy(backbone_presets)
+
+    @classmethod
+    def from_preset(
+        cls,
+        preset,
+        sequence_length=None,
+        **kwargs,
+    ):
+        if preset not in cls.presets:
+            raise ValueError(
+                "`preset` must be one of "
+                f"""{", ".join(cls.presets)}. Received: {preset}."""
+            )
+
+        tokenizer = GPT2Tokenizer.from_preset(preset)
+
+        # Use model's `max_sequence_length` if `sequence_length` unspecified;
+        # otherwise check that `sequence_length` not too long.
+        metadata = cls.presets[preset]
+        max_sequence_length = metadata["config"]["max_sequence_length"]
+        if sequence_length is not None:
+            if sequence_length > max_sequence_length:
+                raise ValueError(
+                    f"`sequence_length` cannot be longer than `{preset}` "
+                    f"preset's `max_sequence_length` of {max_sequence_length}. "
+                    f"Received: {sequence_length}."
+                )
+        else:
+            sequence_length = max_sequence_length
+
+        return cls(
+            tokenizer=tokenizer,
+            sequence_length=sequence_length,
+            **kwargs,
+        )
+
+
+class GPT2CausalLMPreprocessor(GPT2Preprocessor):
+    def call(self, x, y=None, sample_weight=None):
+        token_ids = self.tokenizer(x)
+        mask = tf.ones_like(token_ids, dtype=tf.bool)
+        mask = mask.to_tensor(shape=(None, self.sequence_length))
+        token_ids = token_ids.to_tensor(shape=(None, self.sequence_length))
+        x = {
+            "token_ids": token_ids[:, :-1],
+            "padding_mask": mask[:, 1:],
+        }
+
+        y = token_ids[:, 1:]
+        sample_weight = mask[:, 1:]
+
+        return pack_x_y_sample_weight(x, y, sample_weight)

keras_nlp/samplers/__init__.py

@@ -12,4 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from keras_nlp.samplers.beam_sampler import BeamSampler
 from keras_nlp.samplers.greedy_sampler import GreedySampler
+from keras_nlp.samplers.top_k_sampler import TopKSampler
+from keras_nlp.samplers.top_p_sampler import TopPSampler

keras_nlp/samplers/top_k_sampler → keras_nlp/samplers/top_k_sampler.py

@@ -14,6 +14,7 @@
 """Greedy Sampler."""
 
 import tensorflow as tf
+from tensorflow import keras
 
 from keras_nlp.samplers.sampler import Sampler
 from keras_nlp.samplers.sampler import base_sampler_keyword_args