commit 4575010943c7a6013fad39a9c31e07e3c498a3ce
author Raymond Hettinger <python@rcn.com> Sat Jun 21 11:27:36 2014 -0700
committer Raymond Hettinger <python@rcn.com> Sat Jun 21 11:27:36 2014 -0700
tree 15f224cdbcca568e0be6d6fed374e126638049e9
parent 94919a44a26b135108788f5a7bd5604189c3febe

Issue 21635:  Fix caching in difflib.SequenceMatcher.get_matching_blocks().

Lib/test/test_difflib.py

diff --git a/Lib/test/test_difflib.py b/Lib/test/test_difflib.py
index 310bf99..35f2c36 100644
--- a/Lib/test/test_difflib.py
+++ b/Lib/test/test_difflib.py
@@ -59,6 +59,15 @@
         diff_gen = difflib.unified_diff([], [])
         self.assertRaises(StopIteration, diff_gen.next)
 
+    def test_matching_blocks_cache(self):
+        # Issue #21635
+        s = difflib.SequenceMatcher(None, "abxcd", "abcd")
+        first = s.get_matching_blocks()
+        second = s.get_matching_blocks()
+        self.assertEqual(second[0].size, 2)
+        self.assertEqual(second[1].size, 2)
+        self.assertEqual(second[2].size, 0)
+
     def test_added_tab_hint(self):
         # Check fix for bug #1488943
         diff = list(difflib.Differ().compare(["\tI am a buggy"],["\t\tI am a bug"]))