= Creating bitmap Barcodes in Django with the !ReportLab library =

This describes a simple way to create dynamic bitmap Barcodes in Django.  

!ReportLab's PDF library is well known, but less people are aware that it contains a
mature graphics package able to create most kinds of business charts, as well as custom graphical widgets.

= Installation =
You will need the !ReportLab library from http://www.reportlab.com/

Also make sure you have compiled the ''_rl_accel'' and ''_renderPM'' packages.  The latter
is a sophisticated bitmap renderer with anti-aliasing, font handling and so on.
!ReportLab's download page has a checker script to tell you what extensions
are installed.

= Creating a Barcode =
The reportlab/graphics framework provides a Drawing object and many Shape objects,
which include primitive shapes, and high-level objects like charts, barcodes and legends.  You
can easily write your own too if you want to make dynamic bitmap buttons or fancy
dashboard apps.

The usual pattern we follow is to create a Drawing class with all of your widgets, 
some sensible default data, and any visual settings you want.  Here is the example of a Code128 barcode however it would be easy to create a code39 Barcode etc.

{{{
#    mybarcode.py  
from reportlab.graphics.shapes import Drawing, String
from reportlab.graphics.charts.barcharts import HorizontalBarChart

class MyBarcodeDrawing(Drawing):
    def __init__(self, text_value, *args, **kw):
        barcode = createBarcodeDrawing('Code128', value=text_value,  barHeight=10*mm, humanReadable=True)
        Drawing.__init__(self,barcode.width,barcode.height,*args,**kw)       
        self.add(barcode, name='barcode')
        

if __name__=='__main__':
    #use the standard 'save' method to save barcode.gif, barcode.pdf etc
    #for quick feedback while working.
    MyBarcodeDrawing("HELLO WORLD").save(formats=['gif','pdf'],outDir='.',fnRoot='barcode')
}}}


Paste this into a file and execute it; you should get 4 chart files written to 
disk in different formats.

= Integrating into Django =

Now we add a view to our ''views.py''.  This will examine the request
for any dynamic parameters, since there's not much point serving
a chart that doesn't vary.  We'll allow the user to pass in 4
things as GET or POST parameters:  a title, a comma-separated list of numbers,
and the overall width and height of the image.  Everything has a default in
our Drawing class anyway, so we only pass through parameters which are
present.

You then ask the Drawing to render itself to your favourite bitmap format
and generate a response with the right content-type

{{{
def barcode(request):
    #instantiate a drawing object
    import mybarcode
    d = mybarcode.MyBarcodeDrawing("HELLO WORLD")
    binaryStuff = d.asString('gif')
    return HttpResponse(binaryStuff, 'image/gif')

}}}

Finally, you need a URL mapping.  In this case I have added this:

{{{
    (r'^barcode/$', 'myapp.views.barcode'),

}}}

Now you can start Django, point your browser at the URL with no arguments,
and should see the barcode.  
  http://localhost:8000/barcode/


= Disclaimer =
The author took this from the django [wiki:Charts] example. However he welcomes feedback.

= Learning more about the barcode library =
The available chart types, widgets and properties are covered in the two
Graphics manuals on this page.  Enjoy!
   http://www.reportlab.org/os_documentation.html

If you have questions about the barcodes rather than the Django integration, 
ask on the reportlab-users list:
  http://two.pairlist.net/mailman/listinfo/reportlab-users