Making charts and output them as images to the browser in Django
Lets say you are working on a website made in Django. And you want to make some nice looking graphs real time, as images from dynamic data. This can be done by using the python 2D graph library matplotlib. The library can be found in the debian package python-matplotlib. A simple graph showing a sine curve, seen to the right, can be generated in regular python using the following code(taken from this example):
from pylab import * t = arange(0.0, 2.0, 0.01) s = sin(2*pi*t) plot(t, s, linewidth=1.0) xlabel('time (s)') ylabel('voltage (mV)') title('About as simple as it gets, folks') grid(True) show()
Output graph to browser from a Django view
If you want to output this graph as a PNG image to the browser from a view in Django, you can store the image in a string buffer and output this buffer using the HttpReponse class in Django and set the mime type to image/png.
from django.http import HttpResponse from matplotlib import pylab from pylab import * import PIL, PIL.Image, StringIO def showimage(request): # Construct the graph t = arange(0.0, 2.0, 0.01) s = sin(2*pi*t) plot(t, s, linewidth=1.0) xlabel('time (s)') ylabel('voltage (mV)') title('About as simple as it gets, folks') grid(True) # Store image in a string buffer buffer = StringIO.StringIO() canvas = pylab.get_current_fig_manager().canvas canvas.draw() pilImage = PIL.Image.fromstring("RGB", canvas.get_width_height(), canvas.tostring_rgb()) pilImage.save(buffer, "PNG") pylab.cose() # Send buffer in a http response the the browser with the mime type image/png set return HttpResponse(buffer.getvalue(), mimetype="image/png")