I feel the description of the subprocess.popen semantics is a little
incomplete/confusing to me, on some points, eg. :
- what does the "shell" argument do on windows, exactly ? The beginning
of the description states that nothing changes (createProcess() is used
in any way), but later "COMSPEC" and "shell" are quoted, and their
effect is unclear on windows...  
-"If cwd is not None, the child’s current directory will be changed to
cwd before it is executed. Note that this directory is not considered
when searching the executable, so you can’t specify the program’s path
relative to cwd." -> maybe we should precise that only the "executable"
argument is concerned, not the 'executable' program name which might be
given as first item in "args" argument (and which is, on the contrary,
searched relatively to "cwd" argument)
-for the "bufsize" argument, it would be handy to precise which buffer
size is set (of which file descriptors exactly ? Of Pipes only ?)

Regards, 
P. Chambon