pitrou> The documentation for PyArg_ParseTuple states that the 
pitrou> "I" code doesn't do any overflow checking. Does it mean 
pitrou> the input parameters can be silently truncated?

I'm sorry, but you're right :-) My patch was wrong. New patch 
introduces functions parse_uid() and parse_gid() doing the right thing 
to get an unsigned uid and gid. I reused the parsing code from 
posix_setgroups().