public/gpt-2/transformers/modeling_flax_pytorch_utils.py

# coding=utf-8
# Copyright 2021 The HuggingFace Inc. team.
#
# 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.
""" PyTorch - Flax general utilities."""


import os
from pickle import UnpicklingError

import numpy as np

import jax.numpy as jnp
import transformers
from flax.serialization import from_bytes
from flax.traverse_util import flatten_dict, unflatten_dict

from .utils import logging


logger = logging.get_logger(__name__)


#####################
# PyTorch => Flax #
#####################


def load_pytorch_checkpoint_in_flax_state_dict(flax_model, pytorch_checkpoint_path, allow_missing_keys=False):
    """Load pytorch checkpoints in a flax model"""
    try:
        import torch  # noqa: F401
    except ImportError:
        logger.error(
            "Loading a PyTorch model in Flax, requires both PyTorch and Flax to be installed. Please see "
            "https://pytorch.org/ and https://flax.readthedocs.io/en/latest/installation.html for installation instructions."
        )
        raise

    pt_path = os.path.abspath(pytorch_checkpoint_path)
    logger.info(f"Loading PyTorch weights from {pt_path}")

    pt_state_dict = torch.load(pt_path, map_location="cpu")
    logger.info(f"PyTorch checkpoint contains {sum(t.numel() for t in pt_state_dict.values()):,} parameters.")

    flax_state_dict = convert_pytorch_state_dict_to_flax(pt_state_dict, flax_model)

    return flax_state_dict


def convert_pytorch_state_dict_to_flax(pt_state_dict, flax_model):
    # convert pytorch tensor to numpy
    pt_state_dict = {k: v.numpy() for k, v in pt_state_dict.items()}

    random_flax_state_dict = flatten_dict(flax_model.params)
    flax_state_dict = {}

    remove_base_model_prefix = (flax_model.base_model_prefix not in flax_model.params) and (
        flax_model.base_model_prefix in set([k.split(".")[0] for k in pt_state_dict.keys()])
    )
    add_base_model_prefix = (flax_model.base_model_prefix in flax_model.params) and (
        flax_model.base_model_prefix not in set([k.split(".")[0] for k in pt_state_dict.keys()])
    )

    # Need to change some parameters name to match Flax names so that we don't have to fork any layer
    for pt_key, pt_tensor in pt_state_dict.items():

        pt_tuple_key = tuple(pt_key.split("."))

        has_base_model_prefix = pt_tuple_key[0] == flax_model.base_model_prefix
        require_base_model_prefix = (flax_model.base_model_prefix,) + pt_tuple_key in random_flax_state_dict

        if remove_base_model_prefix and has_base_model_prefix:
            pt_tuple_key = pt_tuple_key[1:]
        elif add_base_model_prefix and require_base_model_prefix:
            pt_tuple_key = (flax_model.base_model_prefix,) + pt_tuple_key

        # Correctly rename weight parameters
        if pt_tuple_key[-1] in ["weight", "gamma"] and pt_tuple_key[:-1] + ("scale",) in random_flax_state_dict:
            pt_tuple_key = pt_tuple_key[:-1] + ("scale",)
        if pt_tuple_key[-1] == "weight" and pt_tuple_key[:-1] + ("embedding",) in random_flax_state_dict:
            pt_tuple_key = pt_tuple_key[:-1] + ("embedding",)
        elif pt_tuple_key[-1] == "weight" and pt_tensor.ndim == 4 and pt_tuple_key not in random_flax_state_dict:
            # conv layer
            pt_tuple_key = pt_tuple_key[:-1] + ("kernel",)
            pt_tensor = pt_tensor.transpose(2, 3, 1, 0)
        elif pt_tuple_key[-1] == "weight" and pt_tuple_key not in random_flax_state_dict:
            # linear layer
            pt_tuple_key = pt_tuple_key[:-1] + ("kernel",)
            pt_tensor = pt_tensor.T
        elif pt_tuple_key[-1] == "gamma":
            pt_tuple_key = pt_tuple_key[:-1] + ("weight",)
        elif pt_tuple_key[-1] == "beta":
            pt_tuple_key = pt_tuple_key[:-1] + ("bias",)

        if pt_tuple_key in random_flax_state_dict:
            if pt_tensor.shape != random_flax_state_dict[pt_tuple_key].shape:
                raise ValueError(
                    f"PyTorch checkpoint seems to be incorrect. Weight {pt_key} was expected to be of shape "
                    f"{random_flax_state_dict[pt_tuple_key].shape}, but is {pt_tensor.shape}."
                )

        # also add unexpected weight so that warning is thrown
        flax_state_dict[pt_tuple_key] = jnp.asarray(pt_tensor)

    return unflatten_dict(flax_state_dict)


#####################
# Flax => PyTorch #
#####################


def load_flax_checkpoint_in_pytorch_model(model, flax_checkpoint_path):
    """Load flax checkpoints in a PyTorch model"""
    flax_checkpoint_path = os.path.abspath(flax_checkpoint_path)
    logger.info(f"Loading Flax weights from {flax_checkpoint_path}")

    # import correct flax class
    flax_cls = getattr(transformers, "Flax" + model.__class__.__name__)

    # load flax weight dict
    with open(flax_checkpoint_path, "rb") as state_f:
        try:
            flax_state_dict = from_bytes(flax_cls, state_f.read())
        except UnpicklingError:
            raise EnvironmentError(f"Unable to convert {flax_checkpoint_path} to Flax deserializable object. ")

    return load_flax_weights_in_pytorch_model(model, flax_state_dict)


def load_flax_weights_in_pytorch_model(pt_model, flax_state):
    """Load flax checkpoints in a PyTorch model"""

    try:
        import torch  # noqa: F401
    except ImportError:
        logger.error(
            "Loading a Flax weights in PyTorch, requires both PyTorch and Flax to be installed. Please see "
            "https://pytorch.org/ and https://flax.readthedocs.io/en/latest/installation.html for installation instructions."
        )
        raise

    flax_state_dict = flatten_dict(flax_state)
    pt_model_dict = pt_model.state_dict()

    remove_base_model_prefix = (pt_model.base_model_prefix in flax_state) and (
        pt_model.base_model_prefix not in set([k.split(".")[0] for k in pt_model_dict.keys()])
    )
    add_base_model_prefix = (pt_model.base_model_prefix not in flax_state) and (
        pt_model.base_model_prefix in set([k.split(".")[0] for k in pt_model_dict.keys()])
    )

    # keep track of unexpected & missing keys
    unexpected_keys = []
    missing_keys = set(pt_model_dict.keys())

    for flax_key_tuple, flax_tensor in flax_state_dict.items():
        has_base_model_prefix = flax_key_tuple[0] == pt_model.base_model_prefix
        require_base_model_prefix = ".".join((pt_model.base_model_prefix,) + flax_key_tuple) in pt_model_dict

        # adapt flax_key to prepare for loading from/to base model only
        if remove_base_model_prefix and has_base_model_prefix:
            flax_key_tuple = flax_key_tuple[1:]
        elif add_base_model_prefix and require_base_model_prefix:
            flax_key_tuple = (pt_model.base_model_prefix,) + flax_key_tuple

        # rename flax weights to PyTorch format
        if flax_key_tuple[-1] == "kernel" and flax_tensor.ndim == 4 and ".".join(flax_key_tuple) not in pt_model_dict:
            # conv layer
            flax_key_tuple = flax_key_tuple[:-1] + ("weight",)
            flax_tensor = jnp.transpose(flax_tensor, (3, 2, 0, 1))
        elif flax_key_tuple[-1] == "kernel" and ".".join(flax_key_tuple) not in pt_model_dict:
            # linear layer
            flax_key_tuple = flax_key_tuple[:-1] + ("weight",)
            flax_tensor = flax_tensor.T
        elif flax_key_tuple[-1] in ["scale", "embedding"]:
            flax_key_tuple = flax_key_tuple[:-1] + ("weight",)

        flax_key = ".".join(flax_key_tuple)

        if flax_key in pt_model_dict:
            if flax_tensor.shape != pt_model_dict[flax_key].shape:
                raise ValueError(
                    f"Flax checkpoint seems to be incorrect. Weight {flax_key_tuple} was expected"
                    f"to be of shape {pt_model_dict[flax_key].shape}, but is {flax_tensor.shape}."
                )
            else:
                # add weight to pytorch dict
                flax_tensor = np.asarray(flax_tensor) if not isinstance(flax_tensor, np.ndarray) else flax_tensor
                pt_model_dict[flax_key] = torch.from_numpy(flax_tensor)
                # remove from missing keys
                missing_keys.remove(flax_key)
        else:
            # weight is not expected by PyTorch model
            unexpected_keys.append(flax_key)

    pt_model.load_state_dict(pt_model_dict)

    # re-transform missing_keys to list
    missing_keys = list(missing_keys)

    if len(unexpected_keys) > 0:
        logger.warning(
            "Some weights of the Flax model were not used when "
            f"initializing the PyTorch model {pt_model.__class__.__name__}: {unexpected_keys}\n"
            f"- This IS expected if you are initializing {pt_model.__class__.__name__} from a Flax model trained on another task "
            "or with another architecture (e.g. initializing a BertForSequenceClassification model from a FlaxBertForPreTraining model).\n"
            f"- This IS NOT expected if you are initializing {pt_model.__class__.__name__} from a Flax model that you expect "
            "to be exactly identical (e.g. initializing a BertForSequenceClassification model from a FlaxBertForSequenceClassification model)."
        )
    else:
        logger.warning(f"All Flax model weights were used when initializing {pt_model.__class__.__name__}.\n")
    if len(missing_keys) > 0:
        logger.warning(
            f"Some weights of {pt_model.__class__.__name__} were not initialized from the Flax model "
            f"and are newly initialized: {missing_keys}\n"
            "You should probably TRAIN this model on a down-stream task to be able to use it for predictions and inference."
        )
    else:
        logger.warning(
            f"All the weights of {pt_model.__class__.__name__} were initialized from the Flax model.\n"
            "If your task is similar to the task the model of the checkpoint was trained on, "
            f"you can already use {pt_model.__class__.__name__} for predictions without further training."
        )

    return pt_model