Fix lemmatizer ordering, re Issue #1387

spacy/lemmatizer.py

@@ -93,7 +93,6 @@ def lemmatize(string, index, exceptions, rules):
     orig = string
     string = string.lower()
     forms = []
-    forms.extend(exceptions.get(string, []))
     oov_forms = []
     for old, new in rules:
         if string.endswith(old):
@@ -104,8 +103,18 @@ def lemmatize(string, index, exceptions, rules):
                 forms.append(form)
             else:
                 oov_forms.append(form)
+    # Remove duplicates, and sort forms generated by rules alphabetically.
+    forms = list(set(forms))
+    forms.sort()
+    # Put exceptions at the front of the list, so they get priority.
+    # This is a dodgy heuristic -- but it's the best we can do until we get
+    # frequencies on this. We can at least prune out problematic exceptions,
+    # if they shadow more frequent analyses.
+    for form in exceptions.get(string, []):
+        if form not in forms:
+            forms.insert(0, form)
     if not forms:
         forms.extend(oov_forms)
     if not forms:
         forms.append(orig)
-    return list(set(forms))
+    return forms