spaCy/spacy/ml/tb_framework.py

from thinc.api import Model, noop
from .parser_model import ParserStepModel


def TransitionModel(
    tok2vec, lower, upper, resize_output, dropout=0.2, unseen_classes=set()
):
    """Set up a stepwise transition-based model"""
    if upper is None:
        has_upper = False
        upper = noop()
    else:
        has_upper = True
    # don't define nO for this object, because we can't dynamically change it
    return Model(
        name="parser_model",
        forward=forward,
        dims={"nI": tok2vec.maybe_get_dim("nI")},
        layers=[tok2vec, lower, upper],
        refs={"tok2vec": tok2vec, "lower": lower, "upper": upper},
        init=init,
        attrs={
            "has_upper": has_upper,
            "unseen_classes": set(unseen_classes),
            "resize_output": resize_output,
        },
    )


def forward(model, X, is_train):
    step_model = ParserStepModel(
        X,
        model.layers,
        unseen_classes=model.attrs["unseen_classes"],
        train=is_train,
        has_upper=model.attrs["has_upper"],
    )

    return step_model, step_model.finish_steps


def init(model, X=None, Y=None):
    model.get_ref("tok2vec").initialize(X=X)
    lower = model.get_ref("lower")
    lower.initialize()
    if model.attrs["has_upper"]:
        statevecs = model.ops.alloc2f(2, lower.get_dim("nO"))
        model.get_ref("upper").initialize(X=statevecs)