code: def set_tcp_md5sig(s, addr, key):
      
      impls = {
          'FreeBSD': _set_tcp_md5sig_bsd,
          'Linux': _set_tcp_md5sig_linux,
          'NetBSD': _set_tcp_md5sig_bsd,
      }
      system = platform.system()
      try:
          impl = impls[system]
      except KeyError:
          raise NotImplementedError("TCP-MD5 unsupported on this platform")
      impl(s, addr, key)
docs: Enable TCP-MD5 on the given socket.
  
      :param s: Socket
      :param addr: Associated address.  On some platforms, this has no effect.
      :param key: Key.  On some platforms, this has no effect.