code: def assert_not_in(self, actual_collection_or_string, unexpected_value,
                        failure_message='Expected "{1}" not to be in "{0}"'):
          
          assertion = lambda: unexpected_value not in actual_collection_or_string
          self.webdriver_assert(assertion, unicode(failure_message).format(actual_collection_or_string, unexpected_value))
docs: Calls smart_assert, but creates its own assertion closure using
          the expected and provided values with the 'not in' operator