Generating a Code39 Barcode

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

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.

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).