[Tutor] popen()ed file object hangs on close() -- why?

[Evgeny Roubinchtein]

So, I have written a very simple script to filter the output of a command.  
Right now it is just the ping command, but I think I can add more. The
problem is the script hangs.  I realize that the ping command is
still writing data when I try to close the pipe.  If I knew it's PID, I 
could try killing it, but I how do I get its PID?  (short of an
equivalent of 'ps ax | grep ping' ) Here is the script:
It hangs under both Linux and FreeBSD, in case that matters.

I know I am doing sthg stupid, I just wish I knew what...

Any help is greatly appreciated

---%<-----

#! /usr/local/bin/python 

import re, os, string, sys

ping = '/bin/ping'
host = '127.0.0.1'
ping_re = r'\s+time=(?P<numbers>\d+\.\d*)\s+ms'

class CommandPipe:
    def __init__(self, command, command_options, command_args, regexp):
        self.prog = string.join((command, command_options, command_args), ' ')
        self.re_obj = re.compile(regexp)
        self.line = ''
    def run(self):
        command_pipe = os.popen(self.prog)
        maxcount = 5  # this can be adjusted
        for i in range(maxcount):
            line = command_pipe.readline()
            if not line:
                break
            line = string.strip(line)
            m = self.re_obj.search(line)
            if m:
                for group in m.groups():
                    print group,
                print # a blank line
        sys.stdout.flush()
        command_pipe.close()  # the script hangs here
        return
        

                
class PingPipe(CommandPipe):
    def __init__(self, command=ping, command_options='', command_args=host,
                 regexp=ping_re):
        CommandPipe.__init__(self, command, command_options, command_args,
                             regexp)
        
def test():
    p = PingPipe()
    p.run()


if __name__=='__main__':
    test()
    sys.exit(0)



--
Evgeny Roubinchtein, eroubinc@u.washington.edu
...................
SDD: Scratch Disk and Die