establish transport connection

def _connect(self):
        """ establish transport connection """

        if self.recvConn:
            if self.pid != os.getpid():
                raise UseAfterFork(
                    "do not re-use a connection after fork; open a new client instead"
                )
            return

        if self.sockpath is None:
            self.sockpath = self._resolvesockname()

        kwargs = {}
        if self.transport == CLIProcessTransport:
            kwargs["binpath"] = self.binpath

        self.tport = self.transport(self.sockpath, self.timeout, **kwargs)
        self.sendConn = self.sendCodec(self.tport)
        self.recvConn = self.recvCodec(self.tport)
        self.pid = os.getpid()