There is also one hidden field in that form. Try this:
Code:
def get_browser(self):
br = BasicNewsRecipe.get_browser()
if self.username is not None and self.password is not None:
br.open('http://szmobil.sueddeutsche.de/login.php')
br.select_form(nr=0)
br['username'] = self.username
br['password'] = self.password
br['id'] = 'streif'
br.submit()
return br