glebkk

  pidfile = "/tmp/server.pid"

  def check_pid(pid):
    """ Check For the existence of a unix pid. """
    try:
      os.kill(pid, 0)
    except OSError:
      return False
    else:
      return True

  if os.path.isfile(pidfile):
    pid = long(open(pidfile, 'r').read())
    if check_pid(pid):
      print "%s already exists, exiting" % pidfile
      sys.exit()

  pid = str(os.getpid())
  file(pidfile, 'w').write(pid)

  # actual code

  # finish
  os.unlink(pidfile)

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