potential commonmiddleware optimization

[JorisBenschop]

please ignore all this if its stupid, but I was trying to create a 1.10 middleware and learn from existing code. Looking at
django.middleware.common.CommonMiddleware I saw this in process_request

host = request.get_host()
must_prepend = settings.PREPEND_WWW and host and not host.startswith('www.')
redirect_url = ('%s://www.%s' % (request.scheme, host)) if must_prepend else ''

If I understand correctly, this code is ran for each request. Would we not get more performance by setting

redirect_url = ''
if  settings.PREPEND_WWW:
    host = request.get_host()
    if host and not host.startswith('www.')
        redirect_url = ('%s://www.%s' % (request.scheme, host)) 

as this evaluates most of the code only when settings.PREPEND_WWW is true.

Again, maybe I completely misunderstand how python code optimization works. But I hope it helps