from typing import Optional, Iterable, Tuple, List, Callable, TYPE_CHECKING
from thinc.api import chain, Maxout, LayerNorm, Softmax, Linear, zero_init, Model
from thinc.api import MultiSoftmax, list2array
from thinc.api import to_categorical, CosineDistance, L2Distance
from ...util import registry
from ...errors import Errors
from ...attrs import ID
import numpy
from functools import partial
if TYPE_CHECKING:
# This lets us add type hints for mypy etc. without causing circular imports
from ...vocab import Vocab # noqa: F401
from ...tokens import Doc # noqa: F401
@registry.architectures.register("spacy.PretrainVectors.v1")
def create_pretrain_vectors(
maxout_pieces: int, hidden_size: int, loss: str
) -> Callable[["Vocab", Model], Model]:
def create_vectors_objective(vocab: "Vocab", tok2vec: Model) -> Model:
model = build_cloze_multi_task_model(
vocab, tok2vec, hidden_size=hidden_size, maxout_pieces=maxout_pieces
)
model.attrs["loss"] = create_vectors_loss()
return model
def create_vectors_loss() -> Callable:
if loss == "cosine":
distance = CosineDistance(normalize=True, ignore_zeros=True)
return partial(get_vectors_loss, distance=distance)
elif loss == "L2":
distance = L2Distance(normalize=True)
return partial(get_vectors_loss, distance=distance)
else:
raise ValueError(Errors.E906.format(found=loss, supported="'cosine', 'L2'"))
return create_vectors_objective
@registry.architectures.register("spacy.PretrainCharacters.v1")
def create_pretrain_characters(
maxout_pieces: int, hidden_size: int, n_characters: int
) -> Callable[["Vocab", Model], Model]:
def create_characters_objective(vocab: "Vocab", tok2vec: Model) -> Model:
model = build_cloze_characters_multi_task_model(
vocab,
tok2vec,
hidden_size=hidden_size,
maxout_pieces=maxout_pieces,
nr_char=n_characters,
)
model.attrs["loss"] = partial(get_characters_loss, nr_char=n_characters)
return model
return create_characters_objective
def get_vectors_loss(ops, docs, prediction, distance):
"""Compute a loss based on a distance between the documents' vectors and
the prediction.
"""
# The simplest way to implement this would be to vstack the
# token.vector values, but that's a bit inefficient, especially on GPU.
# Instead we fetch the index into the vectors table for each of our tokens,
# and look them up all at once. This prevents data copying.
ids = ops.flatten([doc.to_array(ID).ravel() for doc in docs])
target = docs[0].vocab.vectors.data[ids]
d_target, loss = distance(prediction, target)
return loss, d_target
def get_characters_loss(ops, docs, prediction, nr_char):
"""Compute a loss based on a number of characters predicted from the docs."""
target_ids = numpy.vstack([doc.to_utf8_array(nr_char=nr_char) for doc in docs])
target_ids = target_ids.reshape((-1,))
target = ops.asarray(to_categorical(target_ids, n_classes=256), dtype="f")
target = target.reshape((-1, 256 * nr_char))
diff = prediction - target
loss = (diff ** 2).sum()
d_target = diff / float(prediction.shape[0])
return loss, d_target
def build_multi_task_model(
tok2vec: Model,
maxout_pieces: int,
token_vector_width: int,
nO: Optional[int] = None,
) -> Model:
softmax = Softmax(nO=nO, nI=token_vector_width * 2)
model = chain(
tok2vec,
Maxout(
nO=token_vector_width * 2,
nI=token_vector_width,
nP=maxout_pieces,
dropout=0.0,
),
LayerNorm(token_vector_width * 2),
softmax,
)
model.set_ref("tok2vec", tok2vec)
model.set_ref("output_layer", softmax)
return model
def build_cloze_multi_task_model(
vocab: "Vocab", tok2vec: Model, maxout_pieces: int, hidden_size: int
) -> Model:
nO = vocab.vectors.data.shape[1]
output_layer = chain(
list2array(),
Maxout(
nO=hidden_size,
nI=tok2vec.get_dim("nO"),
nP=maxout_pieces,
normalize=True,
dropout=0.0,
),
Linear(nO=nO, nI=hidden_size, init_W=zero_init),
)
model = chain(tok2vec, output_layer)
model = build_masked_language_model(vocab, model)
model.set_ref("tok2vec", tok2vec)
model.set_ref("output_layer", output_layer)
return model
def build_cloze_characters_multi_task_model(
vocab: "Vocab", tok2vec: Model, maxout_pieces: int, hidden_size: int, nr_char: int
) -> Model:
output_layer = chain(
list2array(),
Maxout(hidden_size, nP=maxout_pieces),
LayerNorm(nI=hidden_size),
MultiSoftmax([256] * nr_char, nI=hidden_size),
)
model = build_masked_language_model(vocab, chain(tok2vec, output_layer))
model.set_ref("tok2vec", tok2vec)
model.set_ref("output_layer", output_layer)
return model
def build_masked_language_model(
vocab: "Vocab", wrapped_model: Model, mask_prob: float = 0.15
) -> Model:
"""Convert a model into a BERT-style masked language model"""
random_words = _RandomWords(vocab)
def mlm_forward(model, docs, is_train):
mask, docs = _apply_mask(docs, random_words, mask_prob=mask_prob)
mask = model.ops.asarray(mask).reshape((mask.shape[0], 1))
output, backprop = model.layers[0](docs, is_train)
def mlm_backward(d_output):
d_output *= 1 - mask
return backprop(d_output)
return output, mlm_backward
def mlm_initialize(model: Model, X=None, Y=None):
wrapped = model.layers[0]
wrapped.initialize(X=X, Y=Y)
for dim in wrapped.dim_names:
if wrapped.has_dim(dim):
model.set_dim(dim, wrapped.get_dim(dim))
mlm_model = Model(
"masked-language-model",
mlm_forward,
layers=[wrapped_model],
init=mlm_initialize,
refs={"wrapped": wrapped_model},
dims={dim: None for dim in wrapped_model.dim_names},
)
mlm_model.set_ref("wrapped", wrapped_model)
return mlm_model
class _RandomWords:
def __init__(self, vocab: "Vocab") -> None:
self.words = [lex.text for lex in vocab if lex.prob != 0.0]
self.probs = [lex.prob for lex in vocab if lex.prob != 0.0]
self.words = self.words[:10000]
self.probs = self.probs[:10000]
self.probs = numpy.exp(numpy.array(self.probs, dtype="f"))
self.probs /= self.probs.sum()
self._cache = []
def next(self) -> str:
if not self._cache:
self._cache.extend(
numpy.random.choice(len(self.words), 10000, p=self.probs)
)
index = self._cache.pop()
return self.words[index]
def _apply_mask(
docs: Iterable["Doc"], random_words: _RandomWords, mask_prob: float = 0.15
) -> Tuple[numpy.ndarray, List["Doc"]]:
# This needs to be here to avoid circular imports
from ...tokens import Doc # noqa: F811
N = sum(len(doc) for doc in docs)
mask = numpy.random.uniform(0.0, 1.0, (N,))
mask = mask >= mask_prob
i = 0
masked_docs = []
for doc in docs:
words = []
for token in doc:
if not mask[i]:
word = _replace_word(token.text, random_words)
else:
word = token.text
words.append(word)
i += 1
spaces = [bool(w.whitespace_) for w in doc]
# NB: If you change this implementation to instead modify
# the docs in place, take care that the IDs reflect the original
# words. Currently we use the original docs to make the vectors
# for the target, so we don't lose the original tokens. But if
# you modified the docs in place here, you would.
masked_docs.append(Doc(doc.vocab, words=words, spaces=spaces))
return mask, masked_docs
def _replace_word(word: str, random_words: _RandomWords, mask: str = "[MASK]") -> str:
roll = numpy.random.random()
if roll < 0.8:
return mask
elif roll < 0.9:
return random_words.next()
else:
return word