nl: use the result as an argument for function call of force_bytes, use the result as an argument for calling the method hashlib.md5, put the result in url. substitute the '%s' in string 'views.decorators.cache.cache_header.%s.%s' with key_prefix and result of the function call,
code: cache_key = 'views.decorators.cache.cache_header.%s.%s' % ( key_prefix , url . hexdigest ( ) )