* 给vocabulary添加遍历方法

fastNLP/core/vocabulary.py

@@ -199,3 +199,6 @@ class Vocabulary(object):
 
     def __repr__(self):
         return "Vocabulary({}...)".format(list(self.word_count.keys())[:5])
+
+    def __iter__(self):
+        return iter(list(self.word_count.keys()))

test/core/test_vocabulary.py

@@ -60,6 +60,15 @@ class TestIndexing(unittest.TestCase):
         vocab.update(text)
         self.assertEqual(text, [vocab.to_word(idx) for idx in [vocab[w] for w in text]])
 
+    def test_iteration(self):
+        vocab = Vocabulary()
+        text = ["FastNLP", "works", "well", "in", "most", "cases", "and", "scales", "well", "in",
+                "works", "well", "in", "most", "cases", "scales", "well"]
+        vocab.update(text)
+        text = set(text)
+        for word in vocab:
+            self.assertTrue(word in text)
+
 
 class TestOther(unittest.TestCase):
     def test_additional_update(self):