Add script to convert tf2.x checkpoint to PyTorch (#5791)

* Add script to convert tf2.x checkpoint to pytorch

The script converts the newer TF2.x checkpoints (as published on their official GitHub: https://github.com/tensorflow/models/tree/master/official/nlp/bert) to Pytorch.

* rename file in order to stay consistent with naming convention

src/transformers/convert_bert_original_tf2_checkpoint_to_pytorch.py

+"""
+This script can be used to convert a head-less TF2.x Bert model to PyTorch,
+as published on the official GitHub: https://github.com/tensorflow/models/tree/master/official/nlp/bert
+
+TF2.x uses different variable names from the original BERT (TF 1.4) implementation.
+The script re-maps the TF2.x Bert weight names to the original names, so the model can be imported with Huggingface/transformer.
+
+You may adapt this script to include classification/MLM/NSP/etc. heads.
+"""
+import argparse
+import logging
+import os
+import re
+
+import tensorflow as tf
+import torch
+
+from transformers import BertConfig, BertModel
+
+
+logging.basicConfig(level=logging.INFO)
+logger = logging.getLogger(__name__)
+
+
+def load_tf2_weights_in_bert(model, tf_checkpoint_path, config):
+    tf_path = os.path.abspath(tf_checkpoint_path)
+    logger.info("Converting TensorFlow checkpoint from {}".format(tf_path))
+    # Load weights from TF model
+    init_vars = tf.train.list_variables(tf_path)
+    names = []
+    arrays = []
+    layer_depth = []
+    for full_name, shape in init_vars:
+        # logger.info("Loading TF weight {} with shape {}".format(name, shape))
+        name = full_name.split("/")
+        if full_name == "_CHECKPOINTABLE_OBJECT_GRAPH" or name[0] in ["global_step", "save_counter"]:
+            logger.info(f"Skipping non-model layer {full_name}")
+            continue
+        if "optimizer" in full_name:
+            logger.info(f"Skipping optimization layer {full_name}")
+            continue
+        if name[0] == "model":
+            # ignore initial 'model'
+            name = name[1:]
+        # figure out how many levels deep the name is
+        depth = 0
+        for _name in name:
+            if _name.startswith("layer_with_weights"):
+                depth += 1
+            else:
+                break
+        layer_depth.append(depth)
+        # read data
+        array = tf.train.load_variable(tf_path, full_name)
+        names.append("/".join(name))
+        arrays.append(array)
+    logger.info(f"Read a total of {len(arrays):,} layers")
+
+    # Sanity check
+    if len(set(layer_depth)) != 1:
+        raise ValueError(f"Found layer names with different depths (layer depth {list(set(layer_depth))})")
+    layer_depth = list(set(layer_depth))[0]
+    if layer_depth != 1:
+        raise ValueError(
+            "The model contains more than just the embedding/encoder layers. This script does not handle MLM/NSP heads."
+        )
+
+    # convert layers
+    logger.info("Converting weights...")
+    for full_name, array in zip(names, arrays):
+        name = full_name.split("/")
+        pointer = model
+        trace = []
+        for i, m_name in enumerate(name):
+            if m_name == ".ATTRIBUTES":
+                # variable names end with .ATTRIBUTES/VARIABLE_VALUE
+                break
+            if m_name.startswith("layer_with_weights"):
+                layer_num = int(m_name.split("-")[-1])
+                if layer_num <= 2:
+                    # embedding layers
+                    # layer_num 0: word_embeddings
+                    # layer_num 1: position_embeddings
+                    # layer_num 2: token_type_embeddings
+                    continue
+                elif layer_num == 3:
+                    # embedding LayerNorm
+                    trace.extend(["embeddings", "LayerNorm"])
+                    pointer = getattr(pointer, "embeddings")
+                    pointer = getattr(pointer, "LayerNorm")
+                elif layer_num > 3 and layer_num < config.num_hidden_layers + 4:
+                    # encoder layers
+                    trace.extend(["encoder", "layer", str(layer_num - 4)])
+                    pointer = getattr(pointer, "encoder")
+                    pointer = getattr(pointer, "layer")
+                    pointer = pointer[layer_num - 4]
+                elif layer_num == config.num_hidden_layers + 4:
+                    # pooler layer
+                    trace.extend(["pooler", "dense"])
+                    pointer = getattr(pointer, "pooler")
+                    pointer = getattr(pointer, "dense")
+            elif m_name == "embeddings":
+                trace.append("embeddings")
+                pointer = getattr(pointer, "embeddings")
+                if layer_num == 0:
+                    trace.append("word_embeddings")
+                    pointer = getattr(pointer, "word_embeddings")
+                elif layer_num == 1:
+                    trace.append("position_embeddings")
+                    pointer = getattr(pointer, "position_embeddings")
+                elif layer_num == 2:
+                    trace.append("token_type_embeddings")
+                    pointer = getattr(pointer, "token_type_embeddings")
+                else:
+                    raise ValueError("Unknown embedding layer with name {full_name}")
+                trace.append("weight")
+                pointer = getattr(pointer, "weight")
+            elif m_name == "_attention_layer":
+                # self-attention layer
+                trace.extend(["attention", "self"])
+                pointer = getattr(pointer, "attention")
+                pointer = getattr(pointer, "self")
+            elif m_name == "_attention_layer_norm":
+                # output attention norm
+                trace.extend(["attention", "output", "LayerNorm"])
+                pointer = getattr(pointer, "attention")
+                pointer = getattr(pointer, "output")
+                pointer = getattr(pointer, "LayerNorm")
+            elif m_name == "_attention_output_dense":
+                # output attention dense
+                trace.extend(["attention", "output", "dense"])
+                pointer = getattr(pointer, "attention")
+                pointer = getattr(pointer, "output")
+                pointer = getattr(pointer, "dense")
+            elif m_name == "_output_dense":
+                # output dense
+                trace.extend(["output", "dense"])
+                pointer = getattr(pointer, "output")
+                pointer = getattr(pointer, "dense")
+            elif m_name == "_output_layer_norm":
+                # output dense
+                trace.extend(["output", "LayerNorm"])
+                pointer = getattr(pointer, "output")
+                pointer = getattr(pointer, "LayerNorm")
+            elif m_name == "_key_dense":
+                # attention key
+                trace.append("key")
+                pointer = getattr(pointer, "key")
+            elif m_name == "_query_dense":
+                # attention query
+                trace.append("query")
+                pointer = getattr(pointer, "query")
+            elif m_name == "_value_dense":
+                # attention value
+                trace.append("value")
+                pointer = getattr(pointer, "value")
+            elif m_name == "_intermediate_dense":
+                # attention intermediate dense
+                trace.extend(["intermediate", "dense"])
+                pointer = getattr(pointer, "intermediate")
+                pointer = getattr(pointer, "dense")
+            elif m_name == "_output_layer_norm":
+                # output layer norm
+                trace.append("output")
+                pointer = getattr(pointer, "output")
+            # weights & biases
+            elif m_name in ["bias", "beta"]:
+                trace.append("bias")
+                pointer = getattr(pointer, "bias")
+            elif m_name in ["kernel", "gamma"]:
+                trace.append("weight")
+                pointer = getattr(pointer, "weight")
+            else:
+                logger.warning(f"Ignored {m_name}")
+        # for certain layers reshape is necessary
+        trace = ".".join(trace)
+        if re.match(r"(\S+)\.attention\.self\.(key|value|query)\.(bias|weight)", trace) or re.match(
+            r"(\S+)\.attention\.output\.dense\.weight", trace
+        ):
+            array = array.reshape(pointer.data.shape)
+        if "kernel" in full_name:
+            array = array.transpose()
+        if pointer.shape == array.shape:
+            pointer.data = torch.from_numpy(array)
+        else:
+            raise ValueError(
+                f"Shape mismatch in layer {full_name}: Model expects shape {pointer.shape} but layer contains shape: {array.shape}"
+            )
+        logger.info(f"Successfully set variable {full_name} to PyTorch layer {trace}")
+    return model
+
+
+def convert_tf2_checkpoint_to_pytorch(tf_checkpoint_path, config_path, pytorch_dump_path):
+    # Instantiate model
+    logger.info(f"Loading model based on config from {config_path}...")
+    config = BertConfig.from_json_file(config_path)
+    model = BertModel(config)
+
+    # Load weights from checkpoint
+    logger.info(f"Loading weights from checkpoint {tf_checkpoint_path}...")
+    load_tf2_weights_in_bert(model, tf_checkpoint_path, config)
+
+    # Save pytorch-model
+    logger.info(f"Saving PyTorch model to {pytorch_dump_path}...")
+    torch.save(model.state_dict(), pytorch_dump_path)
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "--tf_checkpoint_path", type=str, required=True, help="Path to the TensorFlow 2.x checkpoint path."
+    )
+    parser.add_argument(
+        "--bert_config_file",
+        type=str,
+        required=True,
+        help="The config json file corresponding to the BERT model. This specifies the model architecture.",
+    )
+    parser.add_argument(
+        "--pytorch_dump_path",
+        type=str,
+        required=True,
+        help="Path to the output PyTorch model (must include filename).",
+    )
+    args = parser.parse_args()
+    convert_tf2_checkpoint_to_pytorch(args.tf_checkpoint_path, args.bert_config_file, args.pytorch_dump_path)