Add tests for reference loops.

Author: serhiy-storchaka

Lib/test/test_unicodedata.py

@@ -12,7 +12,9 @@
 import sys
 import unicodedata
 import unittest
+import weakref
 from test.support import (
+    gc_collect,
     open_urlresource,
     requires_resource,
     script_helper,
@@ -1338,6 +1340,28 @@ def run_grapheme_break_tests(self, testdata):
                     self.assertEqual([x.start for x in result], breaks[i:-1], comment)
                     self.assertEqual([x.end for x in result], breaks[i+1:], comment)
 
+    def test_reference_loops(self):
+        # Test that reference loops involving GraphemeBreakIterator or
+        # Segment can be broken by the garbage collector.
+        class S(str):
+            pass
+
+        s = S('abc')
+        s.ref = unicodedata.iter_graphemes(s)
+        wr = weakref.ref(s)
+        del s
+        self.assertIsNotNone(wr())
+        gc_collect()
+        self.assertIsNone(wr())
+
+        s = S('abc')
+        s.ref = next(unicodedata.iter_graphemes(s))
+        wr = weakref.ref(s)
+        del s
+        self.assertIsNotNone(wr())
+        gc_collect()
+        self.assertIsNone(wr())
+
 
 if __name__ == "__main__":
     unittest.main()