[Tutor] Reading binary files #2

[etrade.griffiths at dsl.pipex.com]

Hi

following last week's discussion with Bob Gailer about reading unformatted FORTRAN files, I have attached an 
example of the file in ASCII format and the equivalent unformatted version.  Below is some code that works OK until 
it gets to a data item that has no additional associated data, then seems to have got 4 bytes ahead of itself.  I 
though I had trapped this but it appears not.  I think the issue is asociated with "newline" characters or the 
unformatted equivalent.

Thanks in advance

Alun Griffiths
==============================
# Test function to write/read from unformatted files

import sys
import struct

# Read file in one go

in_file = open("test.bin","rb")
data = in_file.read()
in_file.close()

# Initialise

nrec = len(data)
stop = 0
items = []

# Read data until EOF encountered

while stop < nrec:
    
    # extract data structure

    start, stop = stop, stop + struct.calcsize('4s8si4s8s')
    vals = struct.unpack('>4s8si4s8s', data[start:stop])
    items.extend(vals)
    print stop, vals

    # define format of subsequent data

    nval = int(vals[2])

    if vals[3] == 'INTE':
        fmt_string = '>i'
    elif vals[3] == 'CHAR':
        fmt_string = '>8s'
    elif vals[3] == 'LOGI':
        fmt_string = '>i'
    elif vals[3] == 'REAL':
        fmt_string = '>f'
    elif vals[3] == 'DOUB':
        fmt_string = '>d'
    elif vals[3] == 'MESS':
        fmt_string = '>%dd' % nval
    else:
        print "Unknown data type ... exiting"
        print items
        sys.exit(0)

    # extract data
    
    for i in range(0,nval):
        start, stop = stop, stop + struct.calcsize(fmt_string)
        vals = struct.unpack(fmt_string, data[start:stop])
        items.extend(vals)

    # trailing spaces

    if nval > 0:
        start, stop = stop, stop + struct.calcsize('4s')
        vals = struct.unpack('4s', data[start:stop])

# All data read so print items

print items


-------------------------------------------------
Visit Pipex Business: The homepage for UK Small Businesses

Go to http://www.pipex.co.uk/business-services

-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: test.asc
URL: <http://mail.python.org/pipermail/tutor/attachments/20090209/c7b098e9/attachment.asc>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: test.bin
Type: application/octet-stream
Size: 476 bytes
Desc: not available
URL: <http://mail.python.org/pipermail/tutor/attachments/20090209/c7b098e9/attachment.bin>