find_element_by_class_name does not work with python : I am trying to fill out a form, using selenium and python.

I am using find_element_by_class_name in the following code and it is not working. I have no idea why as with java it works...

    url='https://service.mail.com/registration.html'
	driver = webdriver.Chrome('/Users/xxxxx/code/chromedriver')
	driver.get(url)
	driver.find_element_by_class_name("Required userdata-firstname").send_keys("james")

Can anyone assist with that? I REALLY do not want to work with java on that.....