> --- On Fri, 7/24/09, Diez B. Roggisch <de...@nospam.web.de> wrote: > >> From: Diez B. Roggisch <de...@nospam.web.de> >> Subject: Re: Popen >> To: python-list@python.org >> Date: Friday, July 24, 2009, 12:35 PM >> Tim schrieb: >> > Thanks! Yes I mean subprocess.Popen. >> > >> > I was wondering the meaning of "asynchronously" >> > Here is some code I am reading recently: >> > " >> > result = Popen(cmdline,shell=True,stdout=PIPE).stdout >> for line in result.readlines(): >> > if find(line,"Cross") != -1: >> > return >> float(split(line)[-1][0:-1]) " >> > The computation in the program "cmdline" takes a long >> time, at the end of which the results will be output to >> stdout. >> > >> > "asynchronous" seems to mean Popen returns to the >> parent process immediately and the parent and child >> processes continue to be executed. >> > However, if Popen returns immediately to the parent >> process, then there will be nothing in "result", not to >> mention extracting information from the output. Thus it >> seems to me the parent process has to wait till the child >> process finish. >> > >> > So how to understand the meaning of "asynchronous"? >> >> "Asynchronous" means asynchronous - the parent is *not* >> waiting. >> >> Which is the reason that there is (amongst other things) >> the "wait"-method you can call to wait for the child to be >> terminated.
On Fri, Jul 24, 2009 at 9:52 AM, Tim<timlee...@yahoo.com> wrote: > > Thanks! If that is the case, i.e. the parent doesn't wait, is the code in my > last post wrong? "result" could be nothing. No, it will be a subprocess.Popen object representing the spawned process. Both the child process and the parent Python process will then be running simultaneously.This allows the Python program to interact with the subprocess via the Popen object while the subprocess is executing in parallel with Python. The asynchronicity means that the call to the Popen constructor does not wait for the spawned subprocess to terminate before returning the new Popen object to the parent Python program. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
