subprocess module

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  • John Mechaniks
    #1

    subprocess module

    from subprocess import call
    call(['ls', '-l'])

    How do I get the result (not the exit status of the command) of "ls -
    l" into a variable?
    Tags: None
    • Peter Otten
      #2
      Re: subprocess module

      John Mechaniks wrote:
      from subprocess import call
      call(['ls', '-l'])
      >
      How do I get the result (not the exit status of the command) of "ls -
      l" into a variable?
      output = subprocess.Pope n(["ls", "-l"], stdout=subproce ss.PIPE).stdout .read()

      Peter

        Comment

        • sukkopera@gmail.com
          #3
          Re: subprocess module

          On 14 Lug, 10:34, Peter Otten <__pete...@web. dewrote:
          John Mechaniks wrote:
          from subprocess import call
          call(['ls', '-l'])
          >
          How do I get the result (not the exit status of the command) of "ls -
          l" into a variable?
          >
          output = subprocess.Pope n(["ls", "-l"], stdout=subproce ss.PIPE).stdout .read()
          >
          Peter
          Correct, but I would rather use Python's os.listdir() and/or
          os.stat(). Executing a simple ls running a subprocess is overkill.

            Comment

            • John Mechaniks
              #4
              Re: subprocess module

              On Jul 14, 12:34 pm, Peter Otten <__pete...@web. dewrote:
              John Mechaniks wrote:
              from subprocess import call
              call(['ls', '-l'])
              >
              How do I get the result (not the exit status of the command) of "ls -
              l" into a variable?
              >
              output = subprocess.Pope n(["ls", "-l"], stdout=subproce ss.PIPE).stdout .read()
              >
              Peter
              Thanks Peter.

              Just curious

              What difference does the following code makes? What are the advantages
              of the above method over this one?
              output = subprocess.Pope n(['ls', '-l'],
              stdout=subproce ss.PIPE).commun icate()[0]

              Also could someone show an example of using the optional input
              argument for communicate()

                Comment

                • Peter Otten
                  #5
                  Re: subprocess module

                  John Mechaniks wrote:
                  On Jul 14, 12:34 pm, Peter Otten <__pete...@web. dewrote:
                  >John Mechaniks wrote:
                  from subprocess import call
                  call(['ls', '-l'])
                  >>
                  How do I get the result (not the exit status of the command) of "ls -
                  l" into a variable?
                  >>
                  >output = subprocess.Pope n(["ls", "-l"],
                  >stdout=subproc ess.PIPE).stdou t.read()
                  What difference does the following code makes? What are the advantages
                  of the above method over this one?
                  output = subprocess.Pope n(['ls', '-l'],
                  stdout=subproce ss.PIPE).commun icate()[0]
                  Hm, I chose it because it looks cleaner. Looking into the source
                  Popen.communica te() seems to do the following:

                  output = p._fo_read_no_i ntr(p.stdout)
                  p.wait()

                  So there are two differences in this case

                  - communicate() waits for the subprocess to terminate.
                  - stdout.read() is retried if an EINTR occurs (Not sure when this would
                  happen).
                  Also could someone show an example of using the optional input
                  argument for communicate()
                  http://blog.doughellmann.com/2007/07/pymotw-subprocess.html


                  I didn't read it myself, but Doug Hellmann's articles are usually quite
                  good.

                  Peter

                    Comment

                    • John Mechaniks
                      #6
                      Re: subprocess module

                      On Jul 14, 7:44 pm, Peter Otten <__pete...@web. dewrote:
                      John Mechaniks wrote:
                      On Jul 14, 12:34 pm, Peter Otten <__pete...@web. dewrote:
                      John Mechaniks wrote:
                      from subprocess import call
                      call(['ls', '-l'])
                      >
                      How do I get the result (not the exit status of the command) of "ls -
                      l" into a variable?
                      >
                      output = subprocess.Pope n(["ls", "-l"],
                      stdout=subproce ss.PIPE).stdout .read()
                      What difference does the following code makes? What are the advantages
                      of the above method over this one?
                      output = subprocess.Pope n(['ls', '-l'],
                      stdout=subproce ss.PIPE).commun icate()[0]
                      >
                      Hm, I chose it because it looks cleaner. Looking into the source
                      Popen.communica te() seems to do the following:
                      >
                      output = p._fo_read_no_i ntr(p.stdout)  
                      p.wait()            
                      >
                      So there are two differences in this case
                      >
                      - communicate() waits for the subprocess to terminate.
                      - stdout.read() is retried if an EINTR occurs (Not sure when this would
                      happen).
                      >
                      Also could someone show an example of using the optional input
                      argument for communicate()
                      >
                      http://blog.doughellmann.com/2007/07/pymotw-subprocess.html

                      >
                      I didn't read it myself, but Doug Hellmann's articles are usually quite
                      good.
                      >
                      Peter
                      Thanks Peter

                        Comment

                        • Sebastian \lunar\ Wiesner
                          #7
                          Re: subprocess module

                          Peter Otten <__peter__@web. de>:
                          - communicate() waits for the subprocess to terminate.
                          - stdout.read() is retried if an EINTR occurs (Not sure when this would
                          happen).
                          EINTR happens, if the "read" syscall is interrupted by a signal handler.
                          For instance, if a daemon handles SIGUSR to re-read its configuration, and
                          the user issues SIGUSR in exactly that very moment, the daemon wants to
                          read from a pipe, the read attempt would fail with EINTR. Shouldn't happen
                          that often ...

                          --
                          Freedom is always the freedom of dissenters.
                          (Rosa Luxemburg)

                            Comment

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