Stop running a test suit from inside a test case in Python unittest framework

I am using Python 2.7, Selenium Webdriver and unittest framework. I have a test suite containing multiple test cases. I want to be able to stop the test run when a specific test case is failed because it does not make sense to continue it in case of failure of that test case. I tried sys.exit() but it does not work as I want. What else should I try?