docs: def pid(self):
          """The server's PID (None if not running).
          """
          # We can't possibly be running if our base_pathname isn't defined.
          if not self.base_pathname:
              return None
          try:
              pidfile = os.path.join(self.base_pathname, 'postmaster.pid')
              return int(open(pidfile).readline())
          except (IOError, OSError):
              return None