code: def _check_pid_changed(self):
      
      try:
        with open(os.path.join(self._build_root, self._pantsd_pidfile), "r") as f:
          pid_from_file = f.read()
      except IOError:
        return "[no file could be read]"
      if int(pid_from_file) != os.getpid():
        return pid_from_file
      else:
        return False
docs: Reads pidfile and returns False if its PID is ours, else a printable (maybe falsey) value.