Test and fix for Issue #2219 (#2272)

Test and fix for Issue #2219: Token.similarity() failed if single letter

.github/contributors/knoxdw.md

@@ -0,0 +1,106 @@
+# spaCy contributor agreement
+
+This spaCy Contributor Agreement (**"SCA"**) is based on the
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+## Contributor Details
+
+| Field                          | Entry                |
+|------------------------------- | -------------------- |
+| Name                           | Douglas Knox         |
+| Company name (if applicable)   |                      |
+| Title or role (if applicable)  |                      |
+| Date                           | 2018-04-27           |
+| GitHub username                | knoxdw               |
+| Website (optional)             |                      |

spacy/tests/regression/test_issue2219.py

@@ -0,0 +1,18 @@
+# coding: utf8
+from __future__ import unicode_literals
+from ..util import add_vecs_to_vocab, get_doc
+import pytest
+
+@pytest.fixture
+def vectors():
+    return [("a", [1, 2, 3]), ("letter", [4, 5, 6])]
+
+@pytest.fixture
+def vocab(en_vocab, vectors):
+    add_vecs_to_vocab(en_vocab, vectors)
+    return en_vocab
+
+def test_issue2219(vocab, vectors):
+    [(word1, vec1), (word2, vec2)] = vectors
+    doc = get_doc(vocab, words=[word1, word2])
+    assert doc[0].similarity(doc[1]) == doc[1].similarity(doc[0])

spacy/tokens/token.pyx

@@ -155,7 +155,7 @@ cdef class Token:
         """
         if 'similarity' in self.doc.user_token_hooks:
             return self.doc.user_token_hooks['similarity'](self)
-        if hasattr(other, '__len__') and len(other) == 1:
+        if hasattr(other, '__len__') and len(other) == 1 and hasattr(other, "__getitem__"):
             if self.c.lex.orth == getattr(other[0], 'orth', None):
                 return 1.0
         elif hasattr(other, 'orth'):