Add costs property to StepwiseState, to show which moves are gold.

spacy/syntax/parser.pyx

@@ -334,15 +334,16 @@ cdef class Parser:
         self.moves.finalize_state(stcls.c)
         return loss
 
-    def step_through(self, Doc doc):
+    def step_through(self, Doc doc, GoldParse gold=None):
         """Set up a stepwise state, to introspect and control the transition sequence.
 
         Arguments:
             doc (Doc): The document to step through.
+            gold (GoldParse): Optional gold parse
         Returns (StepwiseState):
             A state object, to step through the annotation process.
         """
-        return StepwiseState(self, doc)
+        return StepwiseState(self, doc, gold=gold)
 
     def from_transition_sequence(self, Doc doc, sequence):
         """Control the annotations on a document by specifying a transition sequence
@@ -367,13 +368,19 @@ cdef class StepwiseState:
     cdef readonly StateClass stcls
     cdef readonly Example eg
     cdef readonly Doc doc
+    cdef readonly GoldParse gold
     cdef readonly Parser parser
 
-    def __init__(self, Parser parser, Doc doc):
+    def __init__(self, Parser parser, Doc doc, GoldParse gold=None):
         self.parser = parser
         self.doc = doc
+        if gold:
+            self.gold = gold
+        else:
+            self.gold = GoldParse(doc)
         self.stcls = StateClass.init(doc.c, doc.length)
         self.parser.moves.initialize_state(self.stcls.c)
+        self.parser.moves.preprocess_gold(gold)
         self.eg = Example(
             nr_class=self.parser.moves.n_moves,
             nr_atom=CONTEXT_SIZE,
@@ -406,6 +413,20 @@ cdef class StepwiseState:
         return [self.doc.vocab.strings[self.stcls.c._sent[i].dep]
                 for i in range(self.stcls.c.length)]
 
+    @property
+    def costs(self):
+        '''Find the action-costs for the current state'''
+        self.parser.moves.set_costs(self.eg.c.is_valid, self.eg.c.costs,
+                self.stcls, self.gold)
+        costs = {}
+        for i in range(self.parser.moves.n_moves):
+            if not self.eg.c.is_valid[i]:
+                continue
+            transition = self.parser.moves.c[i]
+            name = self.parser.moves.move_name(transition.move, transition.label)
+            costs[name] = self.eg.c.costs[i]
+        return costs
+
     def predict(self):
         self.eg.reset()
         self.eg.c.nr_feat = self.parser.model.set_featuresC(self.eg.c.atoms, self.eg.c.features,