popen2.Popen4: "wait()" hangs on

[Vivien Mallet]

Hello,

I use popen2.Popen4 and I experienced problems with it. Let me show you with
an example. The following script is called "lines" (it prints lines of
'X'):

---------------------
#!/usr/bin/env python

import sys

for line in range(0, int(sys.argv[1])):
    print "X" * 120
---------------------

In a Python console, I launch it:

---------------------
Python 2.3.4 (#2, Jul  5 2004, 09:15:05)
[GCC 3.3.4 (Debian 1:3.3.4-2)] on linux2
>>> import popen2
>>> f = popen2.Popen4("lines 50000")
>>> f.wait()
---------------------

"f.wait()" doesn't return anything. It just hangs on. "f.poll()" returns -1
all the time, even if "lines 50000" should end within one or two seconds.

My guess is that too many characters are sent to the standard output. I
found a way to deal with this problem:

---------------------
Python 2.3.4 (#2, Jul  5 2004, 09:15:05)
[GCC 3.3.4 (Debian 1:3.3.4-2)] on linux2
>>> import popen2
>>> f = popen2.Popen4("lines 50000")
>>> lines = f.fromchild.readlines()
>>> f.wait()
0
---------------------

It works! But it doesn't work in all cases. It happened to me that
"f.fromchild.readlines()" returns lines before the end of process:
"f.wait()" is then called before the end of the process and it may hang
on...

Finally, I usually write:
---------------------
lines = []
while (f.poll() == -1):
    lines += f.fromchild.readlines()
---------------------
which seems to work in any case.

Is my work-around correct? Is there another one?
And why doesn't "wait()" work well? I suspect problems with full buffers or
unflushed buffers, but I am not sure.

Thank you for your help,
Vivien.