> Set your CODESET to ASCII and watch the surrogate escaping
> begin... seriously, Martin, if you've ever worked with CGI
> or WSGI or FastCGI or SCGI or any of the many other protocols
> that use the OS environment for passing data between processes,
> it doesn't take much imagination to come up with examples
> that fail left and right.
> 
> Here's one (RFC 3875, sections 4.1.7 and 4.1.5):
> 
> LANG = 'en_US.utf8'
> CONTENT_TYPE = 'application/x-www-form-urlencoded'
> QUERY_STRING = 'type=example&name=Löwis'
> PATH_INFO = '/home/löwis/bin/mycgi.py'

I still don't see a *failure* here. AFAICT, it all works correctly.
In particular, I fail to see the advantage of using bytes over using
escaped strings, in terms of correctness. I'm even skeptical that there
is an advantage in terms of usability (and if there is, I'd like to see
a demonstration of that, as well).