Question

Say I write this:

from subprocessing import Popen, STDOUT, PIPE
p = Popen(["myproc"], stderr=STDOUT, stdout=PIPE)

Now if I do

line = p.stdout.readline()

my program waits until the subprocess outputs the next line.

Is there any magic I can do to p.stdout so that I could read the output if it’s there, but just continue otherwise? I’m looking for something like Queue.get_nowait()

I know I can just create a thread for reading p.stdout, but let’s assume I can’t create new threads.

Answer 1

Use the select module in Python’s standard library, see http://docs.python.org/library/select.html . select.select([p.stdout.fileno()], [], [], 0) immediately returns a tuple whose items are three lists: the first one is going to be non-empty if there’s something to read on that file descriptor.