How does os.popen works ?

[Rouk]

Hello, i have a problem with os.popen function.

It seems that the command that is launched must be finished before one 
can read from the pipe which was opened.

I made a script called chld.py that writes several lines on stdout with a 
pause of one second between them.

Following code wait until all lines have been written.
>>> a = os.popen("./chld.py", "r", 0)
>>> a.readline()

How can i do to get the lines as soon as they are written to stdout ?
I havn't found anything about it on the web...

Thanks !