IOError: [Errno 4] Interrupted system call

[Marco]

Hello,every one, I meet a question:

in my old script, I usually use os.popen2() to get info from standard
unix(LinuX) program like ps,ifconfig...

Now, I write a OO-based programme, I still use os.popen2( check
whether mplayer still working via ps command ), but some things I got
the following message:

Traceback (most recent call last):
File "./mkt.py", line 351, in loop_timeout
self.process(self.event.get_next())
File "./mkt.py", line 361, in process
self.player.play(command[1])
File "./mkt.py", line 107, in play
if self.is_playing():
File "./mkt.py", line 78, in is_playing
info = rfd.readlines()
IOError: [Errno 4] Interrupted system call

why? Thank you!