#!/usr/bin/python

#ddfex1.py - DDF Example#1 1.0 - 3 Feb 01
#Basic cross-platform script to view a DDF file's DDR/DR leaders.
#See http://www.3dartist.com/WP/sdts/sdtsnotes.htm#pleng
#  for an explanation.
#Update at http://www.3dartist.com/WP/python/pycode.htm#ddfex
#Created by Bill Allen <dempy@3dartist.com>

#HISTORY:
#2001-02-03: First posted.

#PURPOSE:
#This script is an example to show only how to skim through
#  an SDTS DDF file's DDR and DR records.
#PLATFORM: This code should run on any machine that has Python
#  2.0 installed, but has been tested only under Windows ME.
#  Visit http://www.python.org to learn more about Python, a
#  cross-platform freeware language.

#LICENSE: This code is free software provided as is and without
#  warranty for fitness for any purpose. Use it at your own risk.
#  This code and derivations may be used anywhere, including for
#  commercial application. If used for public purposes, an
#  acknowledgment and a link back would be appreciated.

#NOTE: A print statement means to print to the screen ("standard output").

### BEGIN PROGRAM ###

fn = 'c:/python/demtest/1168CEL0.DDF'   #put your DDF file's name here

print '\nScanning',fn
rc = 0                   #record counter
f = open(fn,'rb')        #may contain binary data, so read binary
r = f.read(5)            #read 1st 5 bytes with record length
rid = f.read(2)          #read 2 more bytes
if rid[1] != 'L':        #if this isn't "L", DDF isn't usable
    print '\tNot a DDF file! ID = \\',ord(rid[1]),'\n'
else:                    #is ordinal so can read non-alphanumeric
    while 1:             #loop forever, exit with break
        rlen = int(r)                   #convert rec length to a number
        r = r + rid + f.read(rlen-7)    #get & append rest of the record
        rc = rc + 1
        if ord(r[-1]) != 30:
            print '\tError: End of rec#',rc,'@',rlen,'=',ord(r[-1]),'\n'
            break
### depart from the loop here to do something with the record
        if rc < 4 or rc > 462:          # * uncomment only one of these 3 *
#       if rc < 4 or rc > 1390:         #use on a 10m DEM CEL0.DDF
#       if rc < 21:                     #use on other DDFs
            print '%4d'%rc,':',r[:24]   #print record leader, not too many
### resume loop
        r = f.read(5)                   #start another record
        if not r:
            print '\tEnd of file\n'
            break
        rid = f.read(2)
        if rid[1] not in ['D','L']:     #has to be a D or L
            print '\tError: Bad rec#',rc+1,'ID = \\',ord(rid[1]),'\n'
            break
f.close()