I don't think I understand popen2() behaviour

[Timothy Grant]

Hi,

I need some enlightenment. For the first time ever, I'm playing with pipes
in python and I must be missing something. I'll paste in a couple of
examples to see if I can explain myself.

>>> import os
>>> x = os.popen('tail -f /var/log/messages')
>>> tail: /var/log/messages: Permission denied
tail: no files remaining

>>> 

OK, so I'd expect that behaviour, as I'm logged in as me, not root.

Now, my understanding of popen2() is that it gives me a file handle to both
stdin and stderr, so since I don't want those error messages popping up on
the screen I tried the following

>>> import popen2
>>> x,y = popen2.popen2('tail -f /var/log/messages')
>>> tail: /var/log/messages: Permission denied
tail: no files remaining

>>>

Now that was unexpected, as I would have thought that the error messages
should have been hidden away in my file object y, and that I wouldn't see
them until I did a y.readlines() or something. However, when I try to access
y, I get the following:

>>> y.readlines()
Traceback (innermost last):
  File "<stdin>", line 1, in ?
IOError: [Errno 9] Bad file descriptor
>>> 

So, obviously I don't understand something, but I'm not even sure what it is
I don't understand yet!

Thanks for your assistance.

-- 
Stand Fast,
    tjg.

Timothy Grant                         tjg at exceptionalminds.com
Red Hat Certified Engineer            www.exceptionalminds.com
Avalon Technology Group, Inc.                   (503) 246-3630
>>>>>>>>>>>>>Linux, because rebooting is *NOT* normal<<<<<<<<<
>>>>This machine was last rebooted:  26 days 22:08 hours ago<<