Issue #13896: Make shelf instances work with 'with' as context managers.

Original patch by Filip Gruszczyński.

Lib/shelve.py

@@ -131,6 +131,12 @@ class Shelf(collections.MutableMapping):
         except KeyError:
             pass
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type, value, traceback):
+        self.close()
+
     def close(self):
         self.sync()
         try:
@@ -147,6 +153,7 @@ class Shelf(collections.MutableMapping):
     def __del__(self):
         if not hasattr(self, 'writeback'):
             # __init__ didn't succeed, so don't bother closing
+            # see http://bugs.python.org/issue1339007 for details
             return
         self.close()
 

Lib/test/test_shelve.py

@@ -148,6 +148,19 @@ class TestCase(unittest.TestCase):
         p2 = d[encodedkey]
         self.assertNotEqual(p1, p2)  # Write creates new object in store
 
+    def test_with(self):
+        d1 = {}
+        with shelve.Shelf(d1, protocol=2, writeback=False) as s:
+            s['key1'] = [1,2,3,4]
+            self.assertEqual(s['key1'], [1,2,3,4])
+            self.assertEqual(len(s), 1)
+        self.assertRaises(ValueError, len, s)
+        try:
+            s['key1']
+        except ValueError:
+            pass
+        else:
+            self.fail('Closed shelf should not find a key')
 
 from test import mapping_tests
 

Misc/NEWS

@@ -39,6 +39,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #13896: Make shelf instances work with 'with' as context managers.
+  Original patch by Filip Gruszczyński.
+
 - Issue #15417: Add support for csh and fish in venv activation scripts.
 
 - Issue #16123: IDLE - deprecate running without a subprocess.