pyonmttok 1.23.0

OpenNMT tokenization library

Python API

pip install pyonmttok

Requirements:

• Python version: >= 3.5

Table of contents

1. Tokenization
2. Subword learning
3. Token API
4. Utilities

Tokenization

Example

>>> import pyonmtok
>>> tokenizer = pyonmttok.Tokenizer("aggressive", joiner_annotate=True)
>>> tokens, _ = tokenizer.tokenize("Hello World!")
>>> tokens
['Hello', 'World', '￭!']

Interface

Constructor

tokenizer = pyonmttok.Tokenizer(
    mode: str,
    *,
    bpe_model_path: str = "",
    bpe_dropout: float = 0,
    vocabulary_path: str = "",
    vocabulary_threshold: int = 0,
    sp_model_path: str = "",
    sp_nbest_size: int = 0,
    sp_alpha: float = 0.1,
    joiner: str = "￭",
    joiner_annotate: bool = False,
    joiner_new: bool = False,
    support_prior_joiners: bool = False,
    spacer_annotate: bool = False,
    spacer_new: bool = False,
    case_feature: bool = False,
    case_markup: bool = False,
    no_substitution: bool = False,
    preserve_placeholders: bool = False,
    preserve_segmented_tokens: bool = False,
    segment_case: bool = False,
    segment_numbers: bool = False,
    segment_alphabet_change: bool = False,
    segment_alphabet: Optional[List[str]] = None)

# Copy constructor.
tokenizer = pyonmttok.Tokenizer(tokenizer: pyonmttok.Tokenizer)

See the documentation for a description of each tokenization option.

Tokenization

# By default, tokenize returns the tokens and features.
tokenizer.tokenize(text: str) -> Tuple[List[str], List[List[str]]]

# The as_token_objects flag can alternatively return Token objects (see below).
tokenizer.tokenize(text: str, as_token_objects=True) -> List[pyonmttok.Token]

# Tokenize a file.
tokenizer.tokenize_file(input_path: str, output_path: str, num_threads: int = 1)

Detokenization

# The detokenize method converts tokens back to a string.
tokenizer.detokenize(
    tokens: Union[List[str], List[pyonmttok.Token]],
    features: Optional[List[List[str]]] = None
) -> str

# The detokenize_with_ranges method also returns a dictionary mapping a token
# index to a range in the detokenized text.
# Set merge_ranges=True to merge consecutive ranges, e.g. subwords of the same
# token in case of subword tokenization.
# Set unicode_ranges=True to return ranges over Unicode characters instead of bytes.
tokenizer.detokenize_with_ranges(
    tokens: Union[List[str], List[pyonmttok.Token]],
    merge_ranges: bool = True,
    unicode_ranges: bool = True
) -> Tuple[str, Dict[int, Pair[int, int]]]

# Detokenize a file.
tokenizer.detokenize_file(input_path: str, output_path: str)

Subword learning

Example

The Python wrapper supports BPE and SentencePiece subword learning through a common interface:

1. Create the subword learner with the tokenization you want to apply, e.g.:

# BPE is trained and applied on the tokenization output before joiner (or spacer) annotations.
tokenizer = pyonmttok.Tokenizer("aggressive", joiner_annotate=True, segment_numbers=True)
learner = pyonmttok.BPELearner(tokenizer=tokenizer, symbols=32000)

# SentencePiece can learn from raw sentences so a tokenizer in not required.
learner = pyonmttok.SentencePieceLearner(vocab_size=32000, character_coverage=0.98)

2. Feed some raw data:

# Feed detokenized sentences:
learner.ingest("Hello world!")
learner.ingest("How are you?")

# or detokenized text files:
learner.ingest_file("/data/train1.en")
learner.ingest_file("/data/train2.en")

3. Start the learning process:

tokenizer = learner.learn("/data/model-32k")

The returned tokenizer instance can be used to apply subword tokenization on new data.

Interface

# See https://github.com/rsennrich/subword-nmt/blob/master/subword_nmt/learn_bpe.py
# for argument documentation.
learner = pyonmttok.BPELearner(
    tokenizer: Optional[pyonmttok.Tokenizer] = None,  # Defaults to tokenization mode "space".
    symbols: int = 10000,
    min_frequency: int = 2,
    total_symbols: bool = False)

# See https://github.com/google/sentencepiece/blob/master/src/spm_train_main.cc
# for available training options.
learner = pyonmttok.SentencePieceLearner(
    tokenizer: Optional[pyonmttok.Tokenizer] = None,  # Defaults to tokenization mode "none".
    keep_vocab: bool = False,  # Keep the generated vocabulary (model_path will act like model_prefix in spm_train)
    **training_options)

learner.ingest(text: str)
learner.ingest_file(path: str)
learner.ingest_token(token: Union[str, pyonmttok.Token])

learner.learn(model_path: str, verbose: bool = False) -> pyonmttok.Tokenizer

Token API

The Token API allows to tokenize text into pyonmttok.Token objects. This API can be useful to apply some logics at the token level but still retain enough information to write the tokenization on disk or detokenize.

Example

>>> tokenizer = pyonmttok.Tokenizer("aggressive", joiner_annotate=True)
>>> tokens = tokenizer.tokenize("Hello World!", as_token_objects=True)
>>> tokens
[Token('Hello'), Token('World'), Token('!', join_left=True)]
>>> tokens[-1].surface
'!'
>>> tokenizer.serialize_tokens(tokens)[0]
['Hello', 'World', '￭!']
>>> tokens[-1].surface = '.'
>>> tokenizer.serialize_tokens(tokens)[0]
['Hello', 'World', '￭.']
>>> tokenizer.detokenize(tokens)
'Hello World.'

Interface

The pyonmttok.Token class has the following attributes:

• surface: a string, the token value
• type: a pyonmttok.TokenType value, the type of the token
• join_left: a boolean, whether the token should be joined to the token on the left or not
• join_right: a boolean, whether the token should be joined to the token on the right or not
• preserve: a boolean, whether joiners and spacers can be attached to this token or not
• features: a list of string, the features attached to the token
• spacer: a boolean, whether the token is prefixed by a SentencePiece spacer or not (only set when using SentencePiece)
• casing: a pyonmttok.Casing value, the casing of the token (only set when tokenizing with case_feature or case_markup)

The pyonmttok.TokenType enumeration is used to identify tokens that were split by a subword tokenization. The enumeration has the following values:

• TokenType.WORD
• TokenType.LEADING_SUBWORD
• TokenType.TRAILING_SUBWORD

The pyonmttok.Casing enumeration is used to identify the original casing of a token that was lowercased by the case_feature or case_markup tokenization options. The enumeration has the following values:

• Casing.LOWERCASE
• Casing.UPPERCASE
• Casing.MIXED
• Casing.CAPITALIZED
• Casing.NONE

The Tokenizer instances provide methods to serialize or deserialize Token objects:

# Serialize Token objects to strings that can be saved on disk.
tokenizer.serialize_tokens(tokens: List[pyonmttok.Token]) -> Tuple[List[str], List[List[str]]]

# Deserialize strings into Token objects.
tokenizer.deserialize_tokens(
    tokens: List[str],
    features: Optional[List[List[str]]] = None
) -> List[pyonmttok.Token]

Utilities

Interface

# Returns True if the string has the placeholder format.
pyonmttok.is_placeholder(token: str)

# Sets the random seed for reproducible tokenzation.
pyonmttok.set_random_seed(seed: int)