Python中的十六进制转换错误

Question

I have a problem.

I have a page where I send commands to a sensor network.

When I click on this part of code

<a href='javascript:void(send_command_to_network("{{net.id}}", "restartnwk"));'>Restart Network <i class="icon-repeat"></i> </a>

I call a js function, this:

function send_command_to_network(net, command) {
    $.ajax({url: "/networks/" + net + "/send?command=" + command,
    type: "GET",
    async: true,
    dataType: "json",
    success: function(json_response) { 
         var err = json_response['error'];
     if (err) {
       show_alert('error', err);
       return;
     }
     var success = json_response['success'];
     if (success) {
       show_alert('success', success);
       return;
     }
     show_alert('alert', "This should not happen!");
       }
     }); 
    }

This function build a url that recall an handler in the Tornado web server written in python. The handler is this:

class NetworkSendHandler(BaseHandler):
    # Requires authentication 
    @tornado.web.authenticated
    def get(self, nid):
        # Get the command 
        command = self.get_argument('command').upper(); 

        # The dictionary to return
        ret = {}

        #Check if the command is available
        if command not in ['RESTARTNWK']:
            raise tornado.web.HTTPError(404, "Unknown command: " + str(command))


        #Command ZDP-RestartNwk.Request
        if command == 'RESTARTNWK':
            op_group = "A3"
            op_code = "E0"
            packet_meta = "*%s;%s;%s;#"
            pkt_len = hextransform(16, 2)

            packet = packet_meta % (op_group, op_code, pkt_len)
            packet = packet.upper()

            op_group_hex=0xA3
            op_code_hex=0xE0

            cmdjson = packet2json(op_group_hex,op_code_hex, packet)

        self.finish()

I receive this error in the Tornado debug consolle:

Traceback (most recent call last):
  File "/usr/lib/python2.6/site-packages/tornado/web.py", line 988, in _execute
    getattr(self, self.request.method.lower())(*args, **kwargs)
  File "/usr/lib/python2.6/site-packages/tornado/web.py", line 1739, in wrapper
    return method(self, *args, **kwargs)
  File "./wsn.py", line 859, in get
    cmdjson = packet2json(op_group_hex,op_code_hex, packet)
  File "./wsn.py", line 188, in packet2json
    fcs = fcs ^ int('0x' + payload[(i - 1):(i + 1)], 16)
ValueError: invalid literal for int() with base 16: '0x*A'

I think the error is after the calling of packet2json. And I think the error is in a conversion inside the function, because the error says that '0x*A' isn't a valid int. I think the '*' is the error.... How can I resolve this?

EDIT

Sorry, I forgot the functions:

# Transform an integer into a string with HEX symbols in the format that is
# understandable by Quantaservd
def hextransform(data, length):
    data = hex(data).lstrip('0x').rstrip('L')
    assert(len(data) <= length)
    # zero-padding
    data = ('0' * (length - len(data))) + data
    print data
    # Swap 'bytes' in the network ID
    data = list(data)
    for i in range(0, length, 2):
        tmp = data[i]
        data[i] = data[i + 1]
        data[i + 1] = tmp
    # Reverse the whole string (TODO: CHECK) 
    data.reverse()
    data = "".join(data)
    return data


def packet2json(op_group, op_code, payload): 
    #op_group =
    #op_code =
    #payload=""    # stringa ascii 2 char per byte, senza checksum 
    lun = len(payload) / 2
    fcs = op_group ^ op_code ^ lun #fcs = XOR of op_groip, op_code, lenght and  payload
    for i in range(len(payload)):
    if ((i % 2) == 1):
        fcs = fcs ^ int('0x' + payload[(i - 1):(i + 1)], 16)
        print int('0x' + payload[(i - 1):(i + 1)], 16)
    s=cmd_payload(op_group,op_code, lun, payload, fcs)
    #p = r '{"data": "' + s + r '"}'
    p=r'{"data": "'+s+r'"}'
    return p

Answer 1

the problem lies in the packet2json() function:

for i in range(len(payload)):
    if ((i % 2) == 1):
        fcs = fcs ^ int('0x' + payload[(i - 1):(i + 1)], 16)

in your program, you call this function like this:

packet2json(0xa3, 0xe0, '*A3;E0;10;#')

now the loop above will start with the first character (index 0), ignore it because its index is not odd, then go to the second character (index 1) whose index is odd (1%2 == 1). the body of the if statement, uses int('0x' + payload[(i-1):(i+1)], 16) , that is int('0x' + payload[0:2], 16) , that is int('0x*A',16) , which will always crash...

you shall rewrite this packet2json() function to use the correct string indices, or call it correctly without the leading * in the payload.