fastai/text/interpret.py

from ..torch_core import *
from ..basic_data import *
from ..basic_train import *
from ..train import ClassificationInterpretation
import matplotlib.cm as cm

__all__ = ['TextClassificationInterpretation']

def value2rgba(x:float, cmap:Callable=cm.RdYlGn, alpha_mult:float=1.0)->Tuple:
    "Convert a value `x` from 0 to 1 (inclusive) to an RGBA tuple according to `cmap` times transparency `alpha_mult`."
    c = cmap(x)
    rgb = (np.array(c[:-1]) * 255).astype(int)
    a = c[-1] * alpha_mult
    return tuple(rgb.tolist() + [a])

def piece_attn_html(pieces:List[str], attns:List[float], sep:str=' ', **kwargs)->str:
    html_code,spans = ['<span style="font-family: monospace;">'], []
    for p, a in zip(pieces, attns):
        p = html.escape(p)
        c = str(value2rgba(a, alpha_mult=0.5, **kwargs))
        spans.append(f'<span title="{a:.3f}" style="background-color: rgba{c};">{p}</span>')
    html_code.append(sep.join(spans))
    html_code.append('</span>')
    return ''.join(html_code)

def show_piece_attn(*args, **kwargs):
    from IPython.display import display, HTML
    display(HTML(piece_attn_html(*args, **kwargs)))

def _eval_dropouts(mod):
        module_name =  mod.__class__.__name__
        if 'Dropout' in module_name or 'BatchNorm' in module_name: mod.training = False
        for module in mod.children(): _eval_dropouts(module)

class TextClassificationInterpretation(ClassificationInterpretation):
    """Provides an interpretation of classification based on input sensitivity.
    This was designed for AWD-LSTM only for the moment, because Transformer already has its own attentional model.
    """

    def __init__(self, learn: Learner, preds: Tensor, y_true: Tensor, losses: Tensor, ds_type: DatasetType = DatasetType.Valid):
        super(TextClassificationInterpretation, self).__init__(learn,preds,y_true,losses,ds_type)
        self.model = learn.model

    @classmethod
    def from_learner(cls, learn: Learner,  ds_type:DatasetType=DatasetType.Valid, activ:nn.Module=None):
        "Gets preds, y_true, losses to construct base class from a learner"
        preds_res = learn.get_preds(ds_type=ds_type, activ=activ, with_loss=True, ordered=True)
        return cls(learn, *preds_res)

    def intrinsic_attention(self, text:str, class_id:int=None):
        """Calculate the intrinsic attention of the input w.r.t to an output `class_id`, or the classification given by the model if `None`.
        For reference, see the Sequential Jacobian session at https://www.cs.toronto.edu/~graves/preprint.pdf
        """
        self.model.train()
        _eval_dropouts(self.model)
        self.model.zero_grad()
        self.model.reset()
        ids = self.data.one_item(text)[0]
        emb = self.model[0].module.encoder(ids).detach().requires_grad_(True)
        lstm_output = self.model[0].module(emb, from_embeddings=True)
        self.model.eval()
        cl = self.model[1](lstm_output + (torch.zeros_like(ids).byte(),))[0].softmax(dim=-1)
        if class_id is None: class_id = cl.argmax()
        cl[0][class_id].backward()
        attn = emb.grad.squeeze().abs().sum(dim=-1)
        attn /= attn.max()
        tokens = self.data.single_ds.reconstruct(ids[0])
        return tokens, attn

    def html_intrinsic_attention(self, text:str, class_id:int=None, **kwargs)->str:
        text, attn = self.intrinsic_attention(text, class_id)
        return piece_attn_html(text.text.split(), to_np(attn), **kwargs)

    def show_intrinsic_attention(self, text:str, class_id:int=None, **kwargs)->None:
        text, attn = self.intrinsic_attention(text, class_id)
        show_piece_attn(text.text.split(), to_np(attn), **kwargs)

    def show_top_losses(self, k:int, max_len:int=70)->None:
        """
        Create a tabulation showing the first `k` texts in top_losses along with their prediction, actual,loss, and probability of
        actual class. `max_len` is the maximum number of tokens displayed.
        """
        from IPython.display import display, HTML
        items = []
        tl_val,tl_idx = self.top_losses()
        for i,idx in enumerate(tl_idx):
            if k <= 0: break
            k -= 1
            tx,cl = self.data.dl(self.ds_type).dataset[idx]
            cl = cl.data
            classes = self.data.classes
            txt = ' '.join(tx.text.split(' ')[:max_len]) if max_len is not None else tx.text
            tmp = [txt, f'{classes[self.pred_class[idx]]}', f'{classes[cl]}', f'{self.losses[idx]:.2f}',
                   f'{self.preds[idx][cl]:.2f}']
            items.append(tmp)
        items = np.array(items)
        names = ['Text', 'Prediction', 'Actual', 'Loss', 'Probability']
        df = pd.DataFrame({n:items[:,i] for i,n in enumerate(names)}, columns=names)
        with pd.option_context('display.max_colwidth', -1):
            display(HTML(df.to_html(index=False)))