Fix Issue #371: Lexeme objects were unhashable.

spacy/lexeme.pyx

@@ -68,6 +68,9 @@ cdef class Lexeme:
         else:
             raise NotImplementedError(op)
 
+    def __hash__(self):
+        return self.c.orth
+
     def set_flag(self, attr_id_t flag_id, bint value):
         Lexeme.c_set_flag(self.c, flag_id, value)
     

spacy/tests/vocab/test_lexeme.py

@@ -30,3 +30,13 @@ def test_lexeme_lt(en_vocab):
     assert noun < opera
     assert opera > noun
 
+
+def test_lexeme_hash(en_vocab):
+    '''Test that lexemes are hashable.'''
+    phantom = en_vocab['phantom']
+
+    opera = en_vocab['opera']
+
+    lexes = {phantom: phantom, opera: opera}
+    assert lexes[phantom].orth_ == 'phantom'
+    assert lexes[opera].orth_ == 'opera'