Python 2.2.1 and select()

[Derek Martin]

Hi kids!

I've got some code that uses select.select() to capture all the output
of a subprocess (both stdout and stderr, see below).  This code works
as expected on a variety of Fedora systems running Python > 2.4.0, but
on a Debian Sarge system running Python 2.2.1 it's a no-go.  I'm
thinking this is a bug in that particular version of Python, but I'd
like to have confirmation if anyone can provide it.

The behavior I see is this:  the call to select() returns:
[<file corresponding to sub-proc's STDOUT>] [] []

If and only if the total amount of output is greater than the
specified buffer size, then reading on this file hangs indefinitely.
For what it's worth, the program whose output I need to capture with
this generates about 17k of output to STDERR, and about 1k of output
to STDOUT, at essentially random intervals.  But I also ran it with a
test shell script that generates roughly the same amount of output to
each file object, alternating between STDOUT and STDERR, with the same
results.

Yes, I'm aware that this version of Python is quite old, but I don't
have a great deal of control over that (though if this is indeed a
python bug, as opposed to a problem with my implementation, it might
provide some leverage to get it upgraded)...  Thanks in advance for
any help you can provide.  The code in question (quite short) follows:

def capture(cmd):
    buffsize = 8192
    inlist = []
    inbuf = ""
    errbuf = ""

    io = popen2.Popen3(cmd, True, buffsize)
    inlist.append(io.fromchild)
    inlist.append(io.childerr)
    while True:
        ins, outs, excepts = select.select(inlist, [], [])
        for i in ins:
            x = i.read()
            if not x:
                inlist.remove(i)
            else:
                if i == io.fromchild:
                    inbuf += x
                if i == io.childerr:
                    errbuf += x
        if not inlist:
            break
    if io.wait():
        raise FailedExitStatus, errbuf
    return (inbuf, errbuf)

If anyone would like, I could also provide a shell script and a main
program one could use to test this function...

-- 
Derek D. Martin
http://www.pizzashack.org/
GPG Key ID: 0x81CFE75D

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