remove labels from constructor

spacy/pipeline/multitask.pyx

@@ -47,7 +47,7 @@ class MultitaskObjective(Tagger):
     side-objective.
     """
 
-    def __init__(self, vocab, model, name="nn_labeller", *, labels, target):
+    def __init__(self, vocab, model, name="nn_labeller", *, target):
         self.vocab = vocab
         self.model = model
         self.name = name
@@ -67,7 +67,7 @@ class MultitaskObjective(Tagger):
             self.make_label = target
         else:
             raise ValueError(Errors.E016)
-        cfg = {"labels": labels or {}, "target": target}
+        cfg = {"labels": {}, "target": target}
         self.cfg = dict(cfg)
 
     @property
@@ -81,15 +81,18 @@ class MultitaskObjective(Tagger):
     def set_annotations(self, docs, dep_ids):
         pass
 
-    def initialize(self, get_examples, nlp=None):
+    def initialize(self, get_examples, nlp=None, labels=None):
         if not hasattr(get_examples, "__call__"):
             err = Errors.E930.format(name="MultitaskObjective", obj=type(get_examples))
             raise ValueError(err)
-        for example in get_examples():
-            for token in example.y:
-                label = self.make_label(token)
-                if label is not None and label not in self.labels:
-                    self.labels[label] = len(self.labels)
+        if labels is not None:
+            self.labels = labels
+        else:
+            for example in get_examples():
+                for token in example.y:
+                    label = self.make_label(token)
+                    if label is not None and label not in self.labels:
+                        self.labels[label] = len(self.labels)
         self.model.initialize()   # TODO: fix initialization by defining X and Y
 
     def predict(self, docs):

spacy/pipeline/tagger.pyx

@@ -61,14 +61,13 @@ class Tagger(TrainablePipe):
 
     DOCS: https://nightly.spacy.io/api/tagger
     """
-    def __init__(self, vocab, model, name="tagger", *, labels=None):
+    def __init__(self, vocab, model, name="tagger"):
         """Initialize a part-of-speech tagger.
 
         vocab (Vocab): The shared vocabulary.
         model (thinc.api.Model): The Thinc Model powering the pipeline component.
         name (str): The component instance name, used to add entries to the
             losses during training.
-        labels (List): The set of labels. Defaults to None.
 
         DOCS: https://nightly.spacy.io/api/tagger#init
         """
@@ -76,7 +75,7 @@ class Tagger(TrainablePipe):
         self.model = model
         self.name = name
         self._rehearsal_model = None
-        cfg = {"labels": labels or []}
+        cfg = {"labels": []}
         self.cfg = dict(sorted(cfg.items()))
 
     @property