Difference between revisions of "Generating a Code39 Barcode"

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<syntaxhighlight lang=python>
#!/usr/bin/env python
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# -*- coding: utf-8 -*-
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====Line Positions====
====Line Positions====

Latest revision as of 23:46, 11 February 2018

This article is part of the Scripts series.

Here are the Scribus operations you will find examples for in this script:

  • Testing for and using an existing document
  • Creating a number of lines using a standardized scheme (Code 39 specifications)
  • Using valueDialog for user input, also for more than one value per dialog, using the Python split function
  • Some limited testing for valid user input – encodable characters
  • Creating a text frame at a specified relative page location and with a size defined by the barcode width
  • Setting fonts, and font characteristics, such as its size and alignment of text in the frame
  • Using messageBox for user feedback

How this script came to be

The reason for writing this script was that I had already written a script for modifying a form we use, and on this form are barcodes, one of which indicates the type of form, but the other is variable according to the content of the page.

The script creates that custom part, which has a 10-digit number, then underneath is the barcode. By trial and error I determined that this was a Code39 barcode. Unfortunately, the barcode generator in Scribus cannot be scripted, and in fact you cannot make a custom size for the barcode, so I was copying the 10-digit number, then running Barcode generator, then resizing the created code, which is a PostScript creation, so when it's resized, the width of the bars may change. So far it's been Ok, but this might affect the scanning process.

So here is a first attempt, code39.py. I had thought it was rather slow, but rechecking shows acceptable speed on various computers. The first iterations would only generate a code for digits and uppercase letters (plus the start/stop character), but now it's complete.

Oh, Why Not?

In keeping with the way that sometimes scripts keep getting things added, now we have added the ability to print human-readable characters under the code, decided with a third dialog. This takes your entry, creates a text frame as wide as the code but 3 points below the bottom, enters the text, centers it, with an 8-point Deja Vu Sans Book font.

I see examples where the numbers are more spaced out than this, but of course you can make this adjustment afterward according to your own taste, so it helps to have the frame be as wide as the entire code. This is another advantage of doing this as a script rather than with some outside utility that creates an image of the code.

Code39 results.png
I've also added a warning when you try to code a character that this script won't, so you get a message like this:

As written, it stops at the first non-codable character, even though it does show you your entire entry. In this example '^' would also not be encodable.

Code39 error.png

Maybe I've Got It Done Now

The final itch to scratch were those remaining characters, so now the Code 39 set is complete.

The python is a bit clumsy, but it works.

Code39 results2.png

Somebody Please STOP Me!

Ok, now let's make it more flexible. Instead of hard-coded X-Pos and Y-Pos, we'll add the ability to assign these. By using the Python string split function, we can enter both values with one dialog, and for those times when you just want to get it on the page and then move it later, we'll put in some default values. Note the split syntax, and also that it discards however much whitespace there is between your values. These will be strings, so we need to convert to integer.

I also have added a bailout if you run the script with no document open, since otherwise Scribus will just hang when if scribus.haveDoc() fails.

Code39 location.png


#!/usr/bin/env python
# -*- coding: utf-8 -*-

# ****************************************************************************
#  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
#  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.
# ****************************************************************************

# File: code39.py
# Based on postnet2.py originally 2006.03.06  Gregory Pittman
# this version 2010.08.05   © Gregory Pittman, 2010
# encodes numbers and letters, plus all other Code 39 characters

Simple operation.
First dialog asks for your code (numbers and uppercase letters, plus space, period,
-,*,$,/,+,%) i.e., all characters allowed by Code 39, as many characters as you want.
Second dialog asks for height of bars in points.
Third dialog asks for the X-Pos and Y-Pos, separated only be whitespace, no comma!
Fourth dialog confirms that you want to print the characters underneath.
The start/stop character (*) is automatically added and does not show in the 
human-readable sequence.


import scribus
import sys

# first the codes for numbers 0-9
code39 = ['nnswwn','wnsnnw','nwsnnw','wwsnnn','nnswnw','wnswnn','nwswnn','nnsnww','wnsnwn','nwsnwn']
# next add the codes for A-Z
# and these are for the rest

startstop = 'nsnwwn'
narrow = 1.0   # narrow line width
wide = 2.2    # wide line width
b="Black"     #line color

if scribus.haveDoc():
    S = scribus.valueDialog('Code 39','Enter Numbers or Uppercase Letters')
    height = scribus.valueDialog('Code 39','Enter Height of Bars (Points)')
    height = int(height)
    location = scribus.valueDialog('Code 39','Enter New X-Pos Y-Pos\n(No Comma, just space between)', '200  100')
    relpos = location.split()
    relx = int(relpos[0])
    rely = int(relpos[1])
    origx = relx
    humanread = scribus.valueDialog('Code 39','Print Human-Readable Code Too?\n(Any change means no)', 'Yes')

    code = startstop

    for x in S[0:]:
        if x.isdigit():
            xnum = int(x)
            code = code + code39[xnum]
        elif ((ord(x) > 64) and (ord(x) < 91)):   # ord(character) yields the ascii value
	    xnum = ord(x) - 55
	    code = code + code39[xnum]
        elif (ord(x) == 32):                      #  space
            code = code + code39[36]
        elif ((ord(x) == 36) or (ord(x) == 37)):  #  $ and %
            xnum = ord(x) + 1
            code = code + code39[xnum]
        elif ((ord(x) > 44) and (ord(x) < 48)):   #  - . /
            xnum = ord(x) - 6
            code = code + code39[xnum]
        elif (ord(x) == 43):                      #  +
            code = code + code39[42]
        elif (ord(x) == 42):
            code = code + startstop               #  * (adding for completeness)
            scribus.messageBox('OOPS!',S + '\nCode 39 does not encode this character: ' + x,scribus.ICON_WARNING,button1=scribus.BUTTON_OK)

    code = code + startstop

    for y in code[0:]:
        if y == 'n':
            relx = relx + narrow/2
            d = scribus.createLine(relx,rely,relx,rely + height,) #narrow line
            scribus.setLineWidth(narrow, d)
            scribus.setLineColor(b, d)
            scribus.setFillColor(b, d)
            relx = relx + narrow + narrow/2
        elif y == 'w':
            relx = relx + wide/2
            d = scribus.createLine(relx,rely,relx,rely + height,) #wide line
            scribus.setLineWidth(wide, d)
            scribus.setLineColor(b, d)
            scribus.setFillColor(b, d)
            relx = relx + narrow + wide/2
        elif y == 's':                                      #for wide space
            relx = relx + wide
    if (humanread == 'Yes'):
        t = scribus.createText(origx, rely+height+3, relx - origx, 15)
        scribus.setText(S, t)
        scribus.setFont("DejaVu Sans Book", t)
        scribus.setFontSize(8, t)
        scribus.setTextAlignment(scribus.ALIGN_CENTERED, t)


    scribus.messageBox('OOPS!','You must have a document open to run this script',scribus.ICON_WARNING,button1=scribus.BUTTON_OK)

Line Positions

Something worth mentioning here is that the precise position of the endpoints of lines is in the middle of the line. Thus, when I was creating lines of a particular width with very specific spacing in between, I had to account for the width of the lines or otherwise they would encroach on the space, and so you see these weird arithmetic additions in the if/elif loops.

About Code39

Code 39 is a widely used code consisting of a series of narrow and wide black lines, alternating with narrow or wide white spaces. Each character is denoted by a sequence of 5 lines and 4 intervening spaces, with a narrow space in between characters. The digits 0-9 and capital letters A-Z, plus *, hyphen, period, $, /, % and space are defined. The * character is also known as the start/stop character, since all codes should begin and end with it to orient the scanner.

Narrow and wide lines, and narrow and wide spaces have corresponding width values, and the relative ratios are generally 1:2.2 to 1:3 (narrow:wide).