Implement a __contains__ override for extension manager

Change-Id: I027c576e36fc0f4e016b6aec67f585bf2c03bd7b
Closes-Bug: #1374099

stevedore/extension.py

@@ -274,3 +274,8 @@ class ExtensionManager(object):
                 d[e.name] = e
             self._extensions_by_name = d
         return self._extensions_by_name[name]
+
+    def __contains__(self, name):
+        """Return true if name is in list of enabled extensions.
+        """
+        return any(extension.name == name for extension in self.extensions)

stevedore/tests/test_extension.py

@@ -36,6 +36,10 @@ class TestCallback(utils.TestCase):
         e = em['t1']
         self.assertEqual(e.name, 't1')
 
+    def test_contains_by_name(self):
+        em = extension.ExtensionManager('stevedore.test.extension')
+        self.assertEqual('t1' in em, True)
+
     def test_get_by_name_missing(self):
         em = extension.ExtensionManager('stevedore.test.extension')
         try: