problem with logic in reading a binary file

[Bryan.Fodness at gmail.com]

Hello,

I am having trouble writing the code to read a binary string.  I would
like to extract the values for use in a calculation.

Any help would be great.

Here is my function that takes in a string.

def parseSequence(data, start):

    group_num = data[start:start+2]
    element_num = data[start+2:start+4]
    vl_field = data[start+4:start+8]
    length = struct.unpack('hh', vl_field)[0]
    value = data[start+8:(start+8+length)]
    pos = start+8+length
    element = (group_num+element_num)

    if element == '\xfe\xff\x00\xe0':
        data = value

        while start < length:
            group_num = data[start:start+2]
            element_num = data[start+2:start+4]
            vl_field = data[start+4:start+8]
            length = struct.unpack('hh', vl_field)[0]
            value = data[start+8:(start+8+length)]
            start = start+8+length
            element = (group_num+element_num)

            if element == '\xfe\xff\x00\xe0':
                data = value

                while start < length:
                    group_num = data[start:start+2]
                    element_num = data[start+2:start+4]
                    vl_field = data[start+4:start+8]
                    length = struct.unpack('hh', vl_field)[0]
                    value = data[start+8:(start+8+length)]
                    start = start+8+length
                    element = (group_num+element_num)
                    return element, start, value

            else:
                return element, start, value

    else:
        return  element, pos, value

And, here is a sample string (I have split up and indented for
readability).  There is an identifier (\xfe\xff\x00\xe0) followed by
the length of the nested values.


'\xfe\xff\x00\xe0\x18\x02\x00\x00     -length=536
     \n0q\x00\x02\x00\x00\x001
     \n0x\x00\x02\x00\x00\x0010
     \n0\x80\x00\x02\x00\x00\x004
     \n0\xa0\x00\x02\x00\x00\x000
     \x0c0\x04\x00\xe8\x01\x00\x00
     \xfe\xff\x00\xe0p\x00\x00\x00     -length=112
          \n0\x82\x002\x00\x00\x0042.9068704277562\\-392.3545926477\
\189.182112099444
          \n0\x84\x00\x0c\x00\x00\x008.9617062e-1
          \n0\x86\x00\x10\x00\x00\x00127.378510918301
          \x0c0\x06\x00\x02\x00\x00\x001
     \xfe\xff\x00\xe0p\x00\x00\x00     -length=112
          \n0\x82\x002\x00\x00\x0042.9068704277562\\-392.3545926477\
\189.182112099444
          \n0\x84\x00\x0c\x00\x00\x001.629998e-1
          \n0\x86\x00\x10\x00\x00\x0023.159729257873
          \x0c0\x06\x00\x02\x00\x00\x004
     \xfe\xff\x00\xe0t\x00\x00\x00      -length=116
          \n0\x82\x002\x00\x00\x0042.9068704277562\\-392.3545926477\
\189.182112099444
          \n0\x84\x00\x10\x00\x00\x001.26285318894435
          \n0\x86\x00\x10\x00\x00\x00227.690980638769
          \x0c0\x06\x00\x02\x00\x00\x003
     \xfe\xff\x00\xe0t\x00\x00\x00      -length=116
          \n0\x82\x002\x00\x00\x0042.9068704277562\\-392.3545926477\
\189.182112099444
          \n0\x84\x00\x10\x00\x00\x001.52797639111557
          \n0\x86\x00\x10\x00\x00\x00263.433384670643
          \x0c0\x06\x00\x02\x00\x00\x002 ')