Prevent lemmatization of base nouns

Update lemmatizer's base-form check, for change in morphology class.
Closes #903.

spacy/lemmatizer.py

@@ -44,18 +44,16 @@ class Lemmatizer(object):
     def is_base_form(self, univ_pos, morphology=None):
         '''Check whether we're dealing with an uninflected paradigm, so we can
         avoid lemmatization entirely.'''
-        print("Is base form?", univ_pos, morphology)
         morphology = {} if morphology is None else morphology
         others = [key for key in morphology if key not in (POS, 'number', 'pos', 'verbform')]
         true_morph_key = morphology.get('morph', 0)
-        if univ_pos == 'noun' and morphology.get('number') == 'sing' and not others:
+        if univ_pos == 'noun' and morphology.get('Number') == 'sing' and not others:
             return True
-        elif univ_pos == 'verb' and morphology.get('verbform') == 'inf' and not others:
+        elif univ_pos == 'verb' and morphology.get('VerbForm') == 'inf' and not others:
             return True
         elif univ_pos == 'adj' and morphology.get('Degree') == 'pos':
             return True
-        elif true_morph_key in \
-            (VerbForm_inf, VerbForm_none, Number_sing, Degree_pos):
+        elif true_morph_key in (VerbForm_inf, VerbForm_none, Number_sing, Degree_pos):
             return True
         else:
             return False

spacy/tests/regression/test_issue903.py

@@ -0,0 +1,16 @@
+# coding: utf8
+from __future__ import unicode_literals
+
+import pytest
+from ...tokens import Doc
+
+
+@pytest.mark.parametrize('text,tag,lemma',
+    [("anus", "NN", "anus"),
+     ("princess", "NN", "princess")])
+def test_issue912(en_vocab, text, tag, lemma):
+    '''Test base-forms of adjectives are preserved.'''
+    doc = Doc(en_vocab, words=[text])
+    doc[0].tag_ = tag
+    assert doc[0].lemma_ == lemma
+