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Asked: 2026-06-05T16:29:25+00:00

I have a django view generating a bunch of data which I want to

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I have a django view generating a bunch of data which I want to break down into three different charts to be displayed in a template. I can generate the charts one by one and do a simple return HttpResponse() to determine I’m creating them with the right data, etc.

Since this is the first time I’ve used ReportLab, I want to make sure I’m taking the right approach with generating these for presentation in a web app. I can see two different ways to handle this:

  1. Actually pass the binary representation of the charts to the template and assign them to an img tag. (Unfortunately, I’ve been unsuccessful at this so far – when I dump the binary data in the template, it’s empty)

    1. Save the charts as images and reference the static images in the template.

I’m looking for some advice on which approach to take and if possible, some hints at implementation.

For reference, here’s a snippet from the view producing the charts (much of this was built from the DjangoProject wiki sample):

#instantiate a drawing object
import mycharts
d = mycharts.MyBarChartDrawing(width=800, height=500)

d.chart.categoryAxis.categoryNames = ['Pre-Operative Visit', '6-Week Visit', '3-Month Visit ', '6-Month Visit', '12-Month Visit']
d.chart.data = vas_scores_wrapper   

#get a GIF (or PNG, JPG, or whatever)
image_data = d.asString('png')

return HttpResponse(image_data, 'image/gif')
return render_to_response('summaries/study_summary.html', {'patients':patient_list,'query_form':query_form,'image_data':image_data}, context_instance=RequestContext(request))

This will work to produce a BarChart. FWIW, passing ‘image_data’ to the template and dumping it on that template wasn’t displaying anything. Perhaps you can’t pass binary data directly to a template?

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1 Answer

  1. Editorial Team

    I would save the images to the Media directory and pass their paths to the template to be used in img.href. This would help you cache charts for multiple use and make your life easier when debugging.

    However you could always try to do base64 encoding of the images and pass them as binaries to the template but this would make your html slightly larger when rendering (read slow) and requires extra efforts in debugging when you need to. I recommend the first option.

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