Python Index Error List of index out of range

Question

I have a python code which send serial command to a device and get reply from it.

 def control(command):
     serialport= serial.Serial ("/dev/ttyAMA0", 9600, timeout=0.5)
     serialport.write(command)
     return serialport.readlines(1)

I have a dictionary which map some codes to pass in to command . Then i will print the reply out.

response = control(code_map.get(key,None))
print response, type(response)

EDIT: example of the print out is ['\\x03O?0201\\r'] <type 'list'>

After getting the reply, i have to check for some characters in the reply as such:

if "O?" in response[0]:
    if "01" in response[0]:
        if "0100" in response[0]:
            status="off"
        else:
            status="on"
    else:
        status="off"

It works fine if it only reply once. But when there are 2 or more requests, it raise that index error and it won't display the status.

Here is my javascript to post and get reply for status:

        $('#monitor').click(function(){
            setInterval(function(){
                    $('#status_table tr [id^="monitor_"]:checked').each(function () {
                        monitoring($(this).parents('tr'));
                     });
                },15000);
        });

        function monitoring($row) {
            $('#test').append("checked");
            fbType = $row.find('td:nth-child(3)').html();
            fbNum = $row.find('td:nth-child(4)').html();
            eachStatus =$row.find('td:nth-child(5)').attr('id');
            $('#test').append(fbType + ' '+ fbNum+' '+ eachStatus +'<br>');

            $.post('/request', {inputText: fbNum,key_pressed: fbType.toString()}).done(function (reply) {
                if (reply == "on") {
                    $('#status_table tr #status_'+eachStatus).append("on");
                    $('#test').append("on");
                } else if (reply =="off") {
                    $('#status_table tr #'+eachStatus).empty().append("off");
                    $('#test').append("off");
                }
            });
        }

Traceback:

[03/May/2013:14:36:35] HTTP Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/CherryPy-3.2.2-py2.7.egg/cherrypy/_cprequest.py", line 656, in respond
    response.body = self.handler()
  File "/usr/local/lib/python2.7/dist-packages/CherryPy-3.2.2-py2.7.egg/cherrypy/lib/encoding.py", line 188, in __call__
    self.body = self.oldhandler(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/CherryPy-3.2.2-py2.7.egg/cherrypy/_cpdispatch.py", line 34, in __call__
    return self.callable(*self.args, **self.kwargs)
  File "remote_control_keypad_new52.py", line 677, in request
    if "O?" in response[0]:
IndexError: list index out of range

[03/May/2013:14:36:35] HTTP
Request Headers:
  Content-Length: 31
  REFERER: http://localhost:8080/
  HOST: localhost:8080
  ORIGIN: http://localhost:8080
  CONNECTION: Keep-Alive
  Remote-Addr: 127.0.0.1
  ACCEPT: */*
  USER-AGENT: Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-us) AppleWebKit/535+ (KHTML, like Gecko) Version/5.0 Safari/535.22+ Midori/0.4
  X-REQUESTED-WITH: XMLHttpRequest
  ACCEPT-LANGUAGE: en-us;q=0.750
  Content-Type: application/x-www-form-urlencoded; charset=UTF-8
  ACCEPT-ENCODING: gzip, deflate
127.0.0.1 - - [03/May/2013:14:36:35] "POST /request HTTP/1.1" 500 1460 "http://localhost:8080/" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-us) AppleWebKit/535+ (KHTML, like Gecko) Version/5.0 Safari/535.22+ Midori/0.4"
['\x03O?0101\r\x03O?0201\r'] <type 'list'>
on
127.0.0.1 - - [03/May/2013:14:36:36] "POST /request HTTP/1.1" 200 2 "http://localhost:8080/" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-us) AppleWebKit/535+ (KHTML, like Gecko) Version/5.0 Safari/535.22+ Midori/0.4"
Button one is assigned with Response number None
Button one is assigned with Response number None
Button one is assigned with Response number None
output number selected is 01
R!None
R!None
R!None
R!None
Button one is assigned with Response number None
Button one is assigned with Response number None
Button one is assigned with Response number None
output number selected is 02
R!None
R!None
R!None
R!None
[03/May/2013:14:36:50] HTTP Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/CherryPy-3.2.2-py2.7.egg/cherrypy/_cprequest.py", line 656, in respond
    response.body = self.handler()
  File "/usr/local/lib/python2.7/dist-packages/CherryPy-3.2.2-py2.7.egg/cherrypy/lib/encoding.py", line 188, in __call__
    self.body = self.oldhandler(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/CherryPy-3.2.2-py2.7.egg/cherrypy/_cpdispatch.py", line 34, in __call__
    return self.callable(*self.args, **self.kwargs)
  File "remote_control_keypad_new52.py", line 674, in request
    response = comfort_control(code_map.get(key,None))
  File "remote_control_keypad_new52.py", line 639, in comfort_control
    return serialport.readlines(1)
  File "/usr/lib/python2.7/dist-packages/serial/serialposix.py", line 456, in read
    raise SerialException('device reports readiness to read but returned no data (device disconnected?)')
SerialException: device reports readiness to read but returned no data (device disconnected?)

[03/May/2013:14:36:50] HTTP
Request Headers:
  Content-Length: 31
  REFERER: http://localhost:8080/
  HOST: localhost:8080
  ORIGIN: http://localhost:8080
  CONNECTION: Keep-Alive
  Remote-Addr: 127.0.0.1
  ACCEPT: */*
  USER-AGENT: Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-us) AppleWebKit/535+ (KHTML, like Gecko) Version/5.0 Safari/535.22+ Midori/0.4
  X-REQUESTED-WITH: XMLHttpRequest
  ACCEPT-LANGUAGE: en-us;q=0.750
  Content-Type: application/x-www-form-urlencoded; charset=UTF-8
  ACCEPT-ENCODING: gzip, deflate
127.0.0.1 - - [03/May/2013:14:36:50] "POST /request HTTP/1.1" 500 1839 "http://localhost:8080/" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-us) AppleWebKit/535+ (KHTML, like Gecko) Version/5.0 Safari/535.22+ Midori/0.4"
['\x03O?0101\r\x03O?0201\r'] <type 'list'>
on
127.0.0.1 - - [03/May/2013:14:36:51] "POST /request HTTP/1.1" 200 2 "http://localhost:8080/" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-us) AppleWebKit/535+ (KHTML, like Gecko) Version/5.0 Safari/535.22+ Midori/0.4"
^C[03/May/2013:14:36:56] ENGINE Keyboard Interrupt: shutting down bus
[03/May/2013:14:36:56] ENGINE Bus STOPPING

Answer 1

Perhaps your response is an empty list

>>> response = []
>>> response[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range

Perhaps your device is not always fast enough to respond to this

serialport.write(command)
return serialport.readlines(1)

Particularly if you have 2 requests overlapping, you'll need to make sure that your program is supplying them to the device one at a time.