Code 128 barcode does not work properly

[Horst Schottky]

The changing Codes #99 - #100 - #101 are not correct calculated .
Barcodes with more than one code section (e.g. an odd count >5 of digits or letter and digits mixed) causes an error in inkscape and would otherwise not recognized by a scanner.
The code near the line 100 should be changed from

   num = num + (math.abs(num - 102) * 2)

to

  num = 204 - num

Furthermore a two digit Barcde is not optimized in Code 128C but its printed in Code 128A.
A simple change in the regex near line 55 could fix it:
Cange

  for datum in re.findall(r'(?:(?:\d\d){2,})|.', text):

to

  for datum in re.findall(r'(?:(?:\d\d){2,})|(?:^\d\d)|.', text):

here is the complete working Version:

'''
Copyright (C) 2007 Martin Owens

Debugged by Ralf Heinecke & Martin Siepmann 09/07/2007
Debugged by Horst Schottky Feb. 27. 2010

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

'''

from Base import Barcode
import math
import re

map = [ '11011001100','11001101100','11001100110','10010011000','10010001100','10001001100','10011001000','10011000100','10001100100','11001001000','11001000100','11000100100','10110011100','10011011100','10011001110','10111001100','10011101100','10011100110','11001110010','11001011100','11001001110','11011100100','11001110100','11101101110','11101001100','11100101100','11100100110','11101100100','11100110100','11100110010','11011011000','11011000110','11000110110','10100011000','10001011000','10001000110','10110001000','10001101000','10001100010','11010001000','11000101000','11000100010','10110111000','10110001110','10001101110','10111011000','10111000110','10001110110','11101110110','11010001110','11000101110','11011101000','11011100010','11011101110','11101011000','11101000110','11100010110','11101101000','11101100010','11100011010','11101111010','11001000010','11110001010','10100110000','10100001100','10010110000','10010000110','10000101100','10000100110','10110010000','10110000100','10011010000','10011000010','10000110100','10000110010','11000010010','11001010000','11110111010','11000010100','10001111010','10100111100','10010111100','10010011110','10111100100','10011110100','10011110010','11110100100','11110010100','11110010010','11011011110','11011110110','11110110110','10101111000','10100011110','10001011110','10111101000','10111100010','11110101000','11110100010','10111011110','10111101110','11101011110','11110101110','11010000100','11010010000','11010011100','11000111010','11' ]

def mapExtra(sd, chars):
 result = list(sd)
 for char in chars:
  result.append(chr(char))
 result.append('FNC3')
 result.append('FNC2')
 result.append('SHIFT')
 return result

# The mapExtra method is used to slim down the amount
# of pre code and instead we generate the lists
charAB = list(' !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_')
charA = mapExtra(charAB, range(0, 31)) # Offset 64
charB = mapExtra(charAB, range(96, 125)) # Offset -32

class Object(Barcode):
 def encode(self, text):
  result = ''
  blocks = []
  block = ''

  # Split up into sections of numbers, or charicters
  # This makes sure that all the charicters are encoded
  # In the best way posible for Code128
  for datum in re.findall(r'(?:(?:\d\d){2,})|(?:^\d\d)|.', text):
   if len(datum) == 1:
    block = block + datum
   else:
    if block:
     blocks.append(self.bestBlock(block))
     block = ''
    blocks.append( [ 'C', datum ] )

  if block:
   blocks.append(self.bestBlock(block))
   block = '';

  self.inclabel = text
  return self.encodeBlocks(blocks)

 def bestBlock(self, block):
  # If this has lower case then select B over A
  if block.upper() == block:
   return [ 'A', block ]
  return [ 'B', block ]

 def encodeBlocks(self, blocks):
  total = 0
  pos = 0
  encode = '';

  for block in blocks:
   set = block[0]
   datum = block[1]

   # POS : 0, 1
   # A : 101, 103
   # B : 100, 104
   # C : 99, 105
   num = 0;
   if set == 'A':
    num = 103
   elif set == 'B':
    num = 104
   elif set == 'C':
    num = 105

   i = pos
   if pos:
    num = 204 - num
   else:
    i = 1

   total = total + num * i
   encode = encode + map[num]
   pos = pos + 1

   if set == 'A' or set == 'B':
    chars = charB
    if set == 'A':
     chars = charA

    for char in datum:
     total = total + (chars.index(char) * pos)
     encode = encode + map[chars.index(char)]
     pos = pos + 1
   else:
    for char in (datum[i:i+2] for i in range(0, len(datum), 2)):
     total = total + (int(char) * pos)
     encode = encode + map[int(char)]
     pos = pos + 1

  checksum = total % 103
  encode = encode + map[checksum]
  encode = encode + map[106]
  encode = encode + map[107]

  return encode

[Alvin Penner (apenner)]

for testing purposes, could you provide a few examples of codes that work with the new version and previously did not work?

[Horst Schottky (hog)]

The input '12345' causes an error as shown in the attached screenshot '12345_in_old_Bacode128.png'.
The input 'abc1234' causes the same error - also shown in a screenshot 'abc1234_in_old_Barcode128.png'
The output with the fixed Code128.py is shown in the screenshots '12345_in_new_Barcode128.png' and 'abc1234_in_new_Barcode128.png'

The difference of the length in two-digits-input is shown in the screenshot '12_in_old_and_new_Barcode128'

[Alvin Penner (apenner)]

thanks, Horst, committed to bzr 9119.