execute commands and return output

[billiejoex]

Hi all. I'm searching for a portable (working on *nix and win32) function 
that executes a system command and encapsulate its output into a string.
Searching for the web I found this:

os.popen('command').read()

It is perfect but when che command return an error the funciotn returns an 
empy string.
Does it is possible to return stdout and stderr too?

Best regards