fairseq_dictionary.py

# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is ported from fairseq:
# https://github.com/facebookresearch/fairseq
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of the fairseq repo


import os
import re
from collections import Counter
from multiprocessing import Pool
from typing import Iterable, List

import torch


def item(tensor):
    # tpu-comment: making this a no-op for xla devices.
    if torch.is_tensor(tensor) and tensor.device.type == "xla":
        return tensor.detach()
    if hasattr(tensor, "item"):
        return tensor.item()
    if hasattr(tensor, "__getitem__"):
        return tensor[0]
    return tensor


def post_process(sentence: str, symbol: str):
    if symbol == "sentencepiece":
        sentence = sentence.replace(" ", "").replace("\u2581", " ").strip()
    elif symbol == "wordpiece":
        sentence = sentence.replace(" ", "").replace("_", " ").strip()
    elif symbol == "letter":
        sentence = sentence.replace(" ", "").replace("|", " ").strip()
    elif symbol == "silence":
        import re

        sentence = sentence.replace("<SIL>", "")
        sentence = re.sub(" +", " ", sentence).strip()
    elif symbol == "_EOW":
        sentence = sentence.replace(" ", "").replace("_EOW", " ").strip()
    elif symbol in {"subword_nmt", "@@ ", "@@"}:
        if symbol == "subword_nmt":
            symbol = "@@ "
        sentence = (sentence + " ").replace(symbol, "").rstrip()
    elif symbol == "none":
        pass
    elif symbol is not None:
        raise NotImplementedError(f"Unknown post_process option: {symbol}")
    return sentence


SPACE_NORMALIZER = re.compile(r"\s+")


def tokenize_line(line):
    line = SPACE_NORMALIZER.sub(" ", line)
    line = line.strip()
    return line.split()


def _safe_readline(fd) -> str:
    pos = fd.tell()
    while True:
        try:
            return fd.readline()
        except UnicodeDecodeError:
            pos -= 1
            fd.seek(pos)  # search where this character begins


def find_offsets(filename: str, num_chunks: int) -> List[int]:
    """
    given a file and a number of chuncks, find the offsets in the file
    to be able to chunk around full lines.
    """
    with open(filename, "r", encoding="utf-8") as f:
        size = os.fstat(f.fileno()).st_size
        chunk_size = size // num_chunks
        offsets = [0 for _ in range(num_chunks + 1)]
        for i in range(1, num_chunks):
            f.seek(chunk_size * i)
            _safe_readline(f)
            offsets[i] = f.tell()
        offsets[-1] = size
        return offsets


class ChunkLineIterator:
    """
    Iterator to properly iterate over lines of a file chunck.
    """

    def __init__(self, fd, start_offset: int, end_offset: int):
        self._fd = fd
        self._start_offset = start_offset
        self._end_offset = end_offset

    def __iter__(self) -> Iterable[str]:
        self._fd.seek(self._start_offset)
        # next(f) breaks f.tell(), hence readline() must be used
        line = _safe_readline(self._fd)
        while line:
            pos = self._fd.tell()
            # f.tell() does not always give the byte position in the file
            # sometimes it skips to a very large number
            # it is unlikely that through a normal read we go from
            # end bytes to end + 2**32 bytes (4 GB) and this makes it unlikely
            # that the procedure breaks by the undeterministic behavior of
            # f.tell()
            if (
                self._end_offset > 0
                and pos > self._end_offset
                and pos < self._end_offset + 2 ** 32
            ):
                break
            yield line
            line = self._fd.readline()


class Chunker:
    """
    contextmanager to read a chunck of a file line by line.
    """

    def __init__(self, path: str, start_offset: int, end_offset: int):
        self.path = path
        self.start_offset = start_offset
        self.end_offset = end_offset

    def __enter__(self) -> ChunkLineIterator:
        self.fd = open(self.path, "r", encoding="utf-8")
        return ChunkLineIterator(self.fd, self.start_offset, self.end_offset)

    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
        self.fd.close()


class Dictionary:
    """A mapping from symbols to consecutive integers"""

    def __init__(
        self,
        *,  # begin keyword-only arguments
        bos="<s>",
        pad="<pad>",
        eos="</s>",
        unk="<unk>",
        extra_special_symbols=None,
    ):
        self.bos_word, self.unk_word, self.pad_word, self.eos_word = bos, unk, pad, eos
        self.symbols = []
        self.count = []
        self.indices = {}
        self.bos_index = self.add_symbol(bos)
        self.pad_index = self.add_symbol(pad)
        self.eos_index = self.add_symbol(eos)
        self.unk_index = self.add_symbol(unk)
        if extra_special_symbols:
            for s in extra_special_symbols:
                self.add_symbol(s)
        self.nspecial = len(self.symbols)

    def __eq__(self, other):
        return self.indices == other.indices

    def __getitem__(self, idx):
        if idx < len(self.symbols):
            return self.symbols[idx]
        return self.unk_word

    def get_count(self, idx):
        return self.count[idx]

    def __len__(self):
        """Returns the number of symbols in the dictionary"""
        return len(self.symbols)

    def __contains__(self, sym):
        return sym in self.indices

    def index(self, sym):
        """Returns the index of the specified symbol"""
        assert isinstance(sym, str)
        if sym in self.indices:
            return self.indices[sym]
        return self.unk_index

    def string(
        self,
        tensor,
        bpe_symbol=None,
        escape_unk=False,
        extra_symbols_to_ignore=None,
        unk_string=None,
        include_eos=False,
        separator=" ",
    ):
        """Helper for converting a tensor of token indices to a string.

        Can optionally remove BPE symbols or escape <unk> words.
        """
        if torch.is_tensor(tensor) and tensor.dim() == 2:
            return "\n".join(
                self.string(
                    t,
                    bpe_symbol,
                    escape_unk,
                    extra_symbols_to_ignore,
                    include_eos=include_eos,
                )
                for t in tensor
            )

        extra_symbols_to_ignore = set(extra_symbols_to_ignore or [])
        if not include_eos:
            extra_symbols_to_ignore.add(self.eos())

        def token_string(i):
            if i == self.unk():
                if unk_string is not None:
                    return unk_string
                else:
                    return self.unk_string(escape_unk)
            else:
                return self[i]

        if hasattr(self, "bos_index"):
            extra_symbols_to_ignore.add(self.bos())

        sent = separator.join(
            token_string(i)
            for i in tensor
            if item(i) not in extra_symbols_to_ignore
        )

        return post_process(sent, bpe_symbol)

    def unk_string(self, escape=False):
        """Return unknown string, optionally escaped as: <<unk>>"""
        if escape:
            return "<{}>".format(self.unk_word)
        else:
            return self.unk_word

    def add_symbol(self, word, n=1, overwrite=False):
        """Adds a word to the dictionary"""
        if word in self.indices and not overwrite:
            idx = self.indices[word]
            self.count[idx] = self.count[idx] + n
            return idx
        else:
            idx = len(self.symbols)
            self.indices[word] = idx
            self.symbols.append(word)
            self.count.append(n)
            return idx

    def update(self, new_dict):
        """Updates counts from new dictionary."""
        for word in new_dict.symbols:
            idx2 = new_dict.indices[word]
            if word in self.indices:
                idx = self.indices[word]
                self.count[idx] = self.count[idx] + new_dict.count[idx2]
            else:
                idx = len(self.symbols)
                self.indices[word] = idx
                self.symbols.append(word)
                self.count.append(new_dict.count[idx2])

    def finalize(self, threshold=-1, nwords=-1, padding_factor=8):
        """Sort symbols by frequency in descending order, ignoring special ones.

        Args:
            - threshold defines the minimum word count
            - nwords defines the total number of words in the final dictionary,
                including special symbols
            - padding_factor can be used to pad the dictionary size to be a
                multiple of 8, which is important on some hardware (e.g., Nvidia
                Tensor Cores).
        """
        if nwords <= 0:
            nwords = len(self)

        new_indices = dict(zip(self.symbols[: self.nspecial], range(self.nspecial)))
        new_symbols = self.symbols[: self.nspecial]
        new_count = self.count[: self.nspecial]

        c = Counter(
            dict(
                sorted(zip(self.symbols[self.nspecial:], self.count[self.nspecial:]))
            )
        )
        for symbol, count in c.most_common(nwords - self.nspecial):
            if count >= threshold:
                new_indices[symbol] = len(new_symbols)
                new_symbols.append(symbol)
                new_count.append(count)
            else:
                break

        assert len(new_symbols) == len(new_indices)

        self.count = list(new_count)
        self.symbols = list(new_symbols)
        self.indices = new_indices

        self.pad_to_multiple_(padding_factor)

    def pad_to_multiple_(self, padding_factor):
        """Pad Dictionary size to be a multiple of *padding_factor*."""
        if padding_factor > 1:
            i = 0
            while len(self) % padding_factor != 0:
                symbol = "madeupword{:04d}".format(i)
                self.add_symbol(symbol, n=0)
                i += 1

    def bos(self):
        """Helper to get index of beginning-of-sentence symbol"""
        return self.bos_index

    def pad(self):
        """Helper to get index of pad symbol"""
        return self.pad_index

    def eos(self):
        """Helper to get index of end-of-sentence symbol"""
        return self.eos_index

    def unk(self):
        """Helper to get index of unk symbol"""
        return self.unk_index

    @classmethod
    def load(cls, f):
        """Loads the dictionary from a text file with the format:

        ```
        <symbol0> <count0>
        <symbol1> <count1>
        ...
        ```
        """
        d = cls()
        d.add_from_file(f)
        return d

    def add_from_file(self, f):
        """
        Loads a pre-existing dictionary from a text file and adds its symbols
        to this instance.
        """
        if isinstance(f, str):
            try:
                with open(f, "r", encoding="utf-8") as fd:
                    self.add_from_file(fd)
            except FileNotFoundError as fnfe:
                raise fnfe
            except UnicodeError:
                raise Exception(
                    "Incorrect encoding detected in {}, please "
                    "rebuild the dataset".format(f)
                )
            return

        lines = f.readlines()
        indices_start_line = self._load_meta(lines)

        for line in lines[indices_start_line:]:
            try:
                line, field = line.rstrip().rsplit(" ", 1)
                if field == "#fairseq:overwrite":
                    overwrite = True
                    line, field = line.rsplit(" ", 1)
                else:
                    overwrite = False
                count = int(field)
                word = line
                if word in self and not overwrite:
                    raise RuntimeError(
                        "Duplicate word found when loading Dictionary: '{}'. "
                        "Duplicate words can overwrite earlier ones by adding the "
                        "#fairseq:overwrite flag at the end of the corresponding row "
                        "in the dictionary file. If using the Camembert model, please "
                        "download an updated copy of the model file.".format(word)
                    )
                self.add_symbol(word, n=count, overwrite=overwrite)
            except ValueError:
                raise ValueError(
                    f"Incorrect dictionary format, expected '<token> <cnt> [flags]': \"{line}\""
                )

    def _save(self, f, kv_iterator):
        if isinstance(f, str):
            os.makedirs(os.path.dirname(f), exist_ok=True)
            with open(f, "w", encoding="utf-8") as fd:
                return self.save(fd)
        for k, v in kv_iterator:
            print("{} {}".format(k, v), file=f)

    def _get_meta(self):
        return [], []

    def _load_meta(self, lines):
        return 0

    def save(self, f):
        """Stores dictionary into a text file"""
        ex_keys, ex_vals = self._get_meta()
        self._save(
            f,
            zip(
                ex_keys + self.symbols[self.nspecial:],
                ex_vals + self.count[self.nspecial:],
            ),
        )

    def dummy_sentence(self, length):
        t = torch.Tensor(length).uniform_(self.nspecial + 1, len(self)).long()
        t[-1] = self.eos()
        return t

    def encode_line(
        self,
        line,
        line_tokenizer=tokenize_line,
        add_if_not_exist=True,
        consumer=None,
        append_eos=True,
        reverse_order=False,
    ) -> torch.IntTensor:
        words = line_tokenizer(line)
        if reverse_order:
            words = list(reversed(words))
        nwords = len(words)
        ids = torch.IntTensor(nwords + 1 if append_eos else nwords)

        for i, word in enumerate(words):
            if add_if_not_exist:
                idx = self.add_symbol(word)
            else:
                idx = self.index(word)
            if consumer is not None:
                consumer(word, idx)
            ids[i] = idx
        if append_eos:
            ids[nwords] = self.eos_index
        return ids

    @staticmethod
    def _add_file_to_dictionary_single_worker(
        filename,
        tokenize,
        eos_word,
        start_offset,
        end_offset,
    ):
        counter = Counter()
        with Chunker(filename, start_offset, end_offset) as line_iterator:
            for line in line_iterator:
                for word in tokenize(line):
                    counter.update([word])
                counter.update([eos_word])
        return counter

    @staticmethod
    def add_file_to_dictionary(filename, dict, tokenize, num_workers):
        def merge_result(counter):
            for w, c in sorted(counter.items()):
                dict.add_symbol(w, c)

        local_file = filename
        offsets = find_offsets(local_file, num_workers)
        if num_workers > 1:
            chunks = zip(offsets, offsets[1:])
            pool = Pool(processes=num_workers)
            results = []
            for (start_offset, end_offset) in chunks:
                results.append(
                    pool.apply_async(
                        Dictionary._add_file_to_dictionary_single_worker,
                        (
                            local_file,
                            tokenize,
                            dict.eos_word,
                            start_offset,
                            end_offset,
                        ),
                    )
                )
            pool.close()
            pool.join()
            for r in results:
                merge_result(r.get())
        else:
            merge_result(
                Dictionary._add_file_to_dictionary_single_worker(
                    local_file, tokenize, dict.eos_word, offsets[0], offsets[1]
                )
            )