Add add_label methods to Tagger and TextCategorizer

spacy/pipeline.pyx

@@ -11,9 +11,9 @@ import ujson
 import msgpack
 
 from thinc.api import chain
-from thinc.v2v import Softmax
+from thinc.v2v import Affine, Softmax
 from thinc.t2v import Pooling, max_pool, mean_pool
-from thinc.neural.util import to_categorical
+from thinc.neural.util import to_categorical, copy_array
 from thinc.neural._classes.difference import Siamese, CauchySimilarity
 
 from .tokens.doc cimport Doc
@@ -130,6 +130,15 @@ class Pipe(object):
         documents and their predicted scores."""
         raise NotImplementedError
 
+    def add_label(self, label):
+        """Add an output label, to be predicted by the model.
+
+        It's possible to extend pre-trained models with new labels,
+        but care should be taken to avoid the "catastrophic forgetting"
+        problem.
+        """
+        raise NotImplementedError
+
     def begin_training(self, gold_tuples=tuple(), pipeline=None):
         """Initialize the pipe for training, using data exampes if available.
         If no model has been initialized yet, the model is added."""
@@ -325,6 +334,14 @@ class Tagger(Pipe):
         self.cfg.setdefault('pretrained_dims',
                             self.vocab.vectors.data.shape[1])
 
+    @property
+    def labels(self):
+        return self.cfg.setdefault('tag_names', [])
+
+    @labels.setter
+    def labels(self, value):
+        self.cfg['tag_names'] = value
+
     def __call__(self, doc):
         tags = self.predict([doc])
         self.set_annotations([doc], tags)
@@ -352,6 +369,7 @@ class Tagger(Pipe):
         cdef Doc doc
         cdef int idx = 0
         cdef Vocab vocab = self.vocab
+        tags = list(self.labels)
         for i, doc in enumerate(docs):
             doc_tag_ids = batch_tag_ids[i]
             if hasattr(doc_tag_ids, 'get'):
@@ -359,7 +377,7 @@ class Tagger(Pipe):
             for j, tag_id in enumerate(doc_tag_ids):
                 # Don't clobber preset POS tags
                 if doc.c[j].tag == 0 and doc.c[j].pos == 0:
-                    vocab.morphology.assign_tag_id(&doc.c[j], tag_id)
+                    vocab.morphology.assign_tag(&doc.c[j], tags[tag_id])
                 idx += 1
         doc.is_tagged = True
 
@@ -420,6 +438,17 @@ class Tagger(Pipe):
     def Model(cls, n_tags, **cfg):
         return build_tagger_model(n_tags, **cfg)
 
+    def add_label(self, label):
+        if label in self.labels:
+            return 0
+        smaller = self.model[-1]._layers[-1]
+        larger = Softmax(len(self.labels)+1, smaller.nI)
+        copy_array(larger.W[:smaller.nO], smaller.W)
+        copy_array(larger.b[:smaller.nO], smaller.b)
+        self.model[-1]._layers[-1] = larger
+        self.labels.append(label)
+        return 1
+
     def use_params(self, params):
         with self.model.use_params(params):
             yield
@@ -675,7 +704,7 @@ class TextCategorizer(Pipe):
 
     @property
     def labels(self):
-        return self.cfg.get('labels', ['LABEL'])
+        return self.cfg.setdefault('labels', ['LABEL'])
 
     @labels.setter
     def labels(self, value):
@@ -727,6 +756,17 @@ class TextCategorizer(Pipe):
         mean_square_error = ((scores-truths)**2).sum(axis=1).mean()
         return mean_square_error, d_scores
 
+    def add_label(self, label):
+        if label in self.labels:
+            return 0
+        smaller = self.model[-1]._layers[-1]
+        larger = Affine(len(self.labels)+1, smaller.nI)
+        copy_array(larger.W[:smaller.nO], smaller.W)
+        copy_array(larger.b[:smaller.nO], smaller.b)
+        self.model[-1]._layers[-1] = larger
+        self.labels.append(label)
+        return 1
+
     def begin_training(self, gold_tuples=tuple(), pipeline=None):
         if pipeline and getattr(pipeline[0], 'name', None) == 'tensorizer':
             token_vector_width = pipeline[0].model.nO