How to use Matplotlib in Django?

From some examples from the Internet I made the test code below. It works!

... BUT if I reload the page, the pie will draw itself with the same image. Some parts get darker every time I reload the page. When I restart the the development server, it is reset. How do I draw properly with Matplotlib in Django? It looks like it remembers some drawings...

Source views.py (let urls.py link to it):

from pylab import figure, axes, pie, title
from matplotlib.backends.backend_agg import FigureCanvasAgg

def test_matplotlib(request):
    f = figure(1, figsize=(6,6))
    ax = axes([0.1, 0.1, 0.8, 0.8])
    labels = 'Frogs', 'Hogs', 'Dogs', 'Logs'
    fracs = [15,30,45, 10]
    explode=(0, 0.05, 0, 0)
    pie(fracs, explode=explode, labels=labels, autopct='%1.1f%%', shadow=True)
    title('Raining Hogs and Dogs', bbox={'facecolor':'0.8', 'pad':5})

    canvas = FigureCanvasAgg(f)    
    response = HttpResponse(content_type='image/png')
    canvas.print_png(response)
    return response

I am using Django 1.0.1 and Python 2.6.2 (Linux).

You need to remove the num parameter from the figure constructor and close the figure when you're done with it.

import matplotlib.pyplot

def test_matplotlib(request):
    f = figure(figsize=(6,6))
    ....
    matplotlib.pyplot.close(f)

By removing the num parameter, you'll avoid using the same figure at the same time. This could happen if 2 browsers request the image at the same time. If this is not an issue, another possible solution is to use the clear method, i.e. f.clear().