bpo-32234: Context manager available for mailbox instances

Doc/library/mailbox.rst

@@ -76,6 +76,14 @@ Supported mailbox formats are Maildir, mbox, MH, Babyl, and MMDF.
       message.  Failing to lock the mailbox runs the risk of losing messages or
       corrupting the entire mailbox.
 
+   The :class:`Mailbox` class supports the :keyword:`with` statement.  When used
+   like this, the Mailbox acquires a lock when the :keyword:`with` statement
+   enters and releases it and :meth:`close` when the :keyword:`with` statement
+   exits.
+
+   .. versionchanged:: 3.7
+      Support for the :keyword:`with` statement was added.
+
    :class:`Mailbox` instances have the following methods:
 
 

Lib/mailbox.py

@@ -38,6 +38,13 @@ def __init__(self, path, factory=None, create=True):
         self._path = os.path.abspath(os.path.expanduser(path))
         self._factory = factory
 
+    def __enter__(self):
+        self.lock()
+        return self
+
+    def __exit__(self, type, value, traceback):
+        self.close()
+
     def add(self, message):
         """Add message and return assigned key."""
         raise NotImplementedError('Method must be implemented by subclass')

Lib/test/test_mailbox.py

@@ -532,6 +532,11 @@ def _test_flush_or_close(self, method, should_call_close):
             self.assertIn(self._box.get_string(key), contents)
         oldbox.close()
 
+    def test_use_context_manager(self):
+        # Mailboxes are usable as a context manager
+        with self._factory(self._path) as box:
+            self.assertIsInstance(box, self._box.__class__)
+
     def test_dump_message(self):
         # Write message representations to disk
         for input in (email.message_from_string(_sample_message),

Misc/NEWS.d/next/Library/2017-12-15-09-32-57.bpo-32234.XaOkhR.rst

@@ -0,0 +1,2 @@
+Mailbox instances can be used in the context manager. The Mailbox is locked
+at enter and unlocked and closed at exit.