Question

I came across this great replacment for the getstatusoutput() function in Python 2.* which works equally well on Unix and Windows. However, I think there is something wrong with the way the output is constructed. It only returns the last line of the output, but I can’t figure out why. Any help would be awesome.

def getstatusoutput(cmd):
    """Return (status, output) of executing cmd in a shell."""
    """This new implementation should work on all platforms."""
    import subprocess
    pipe = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True, universal_newlines=True)
    output = "".join(pipe.stdout.readlines())
    sts = pipe.returncode
    if sts is None: sts = 0
    return sts, output

Answer 1

There is a bug in this.

The call:

pipe = subprocess.Popen(...)

kicks off the process. The line:

output = "".join(pipe.stdout.readlines())

reads the process’s stdout (if there were error output it could get jammed up, but since you did not redirect stderr this is safe; in the more general case, you need to use the .communicate() function to avoid possible wedging). You might think: well, now that I’ve read all the output, the subprocess has clearly finished, so pipe.returncode should be set. But in fact, if you replace:

sts = pipe.returncode
if sts is None: sts = 0

with code that includes a diagnostic of some sort (or just delete the second line entirely), you’ll find that, at least on some systems sometimes, sts is None. The reason is that the subprocess module has not had a chance to retrieve it yet. You should replace those lines with:

sts = pipe.wait()

to collect the result and obviate the need for the is None test. (It’s safe to call .wait() even if you’ve used .communicate() and/or already called .wait().)

The "".join(...) can be done slightly more efficiently by using just:

output = pipe.stdout.read()

All that said, it does get the full output for me. Perhaps you’re reading from something that uses just '\r' for newlines and your Python was built without universal-newline support? (If I run something that produces \r-for-newline I still get all the lines, separated by actual newlines.)