using different browsers via selenium webdrivers

browsers.py

class ProjectName(unittest.TestCase):
    def __init__(self, browser):
        if browser == "firefox":
            self.driver = webdriver.Firefox()
        elif browser == "ie":
            self.driver = webdriver.Ie()
        elif browser == "chrome":
            self.driver = webdriver.Chrome()
        else:
            print( "browsers: firefox, ie, chrome" )         
            sys.exit()
            
    def sample_test_case(self):
        driver = self.driver
        
        """
        code your test case
        and call it by:
        object = ProjectName("ie")
        
        object.sample_test_case()
        """
        
    def another_test_case(self):
        driver = self.driver
        
        """
        ... test code
        
        """
        
        
if __name__ == "__main__":
    unittest.main()

run.py

import webdriver_browsers.py

test = ProjectName("chrome")

test.sample_test_case()