python 类型错误

即使所有部分都是字符串，我仍收到以下 python 错误

    request = str(self.SETUP) + " " + str(self.fileName) + "RTSP/1.0"; 
TypeError: unsupported operand type(s) for +: 'int' and 'str' 

整段代码:

if requestCode == self.SETUP and self.state == self.INIT: 
    threading.Thread(target=self.recvRtspReply).start() 
    # Update RTSP sequence number. 
    self.rtspSeq = self.rtspSeq + 1 
 
    # Write the RTSP request to be sent. 
    request = str(self.SETUP) + " " + str(self.fileName) + "RTSP/1.0" 
 
 
    # Keep track of the sent request. 
    self.requestSent = request