I am using matplotlib in a django app and would like to directly return the rendered image.
So far I can go plt.savefig(...), then return the location of the image.
What I want to do is:
return HttpResponse(plt.renderfig(...), mimetype="image/png")
Any ideas?
Django's HttpResponse object supports file-like API and you can pass a file-object to savefig.
response = HttpResponse(mimetype="image/png")
# create your image as usual, e.g. pylab.plot(...)
pylab.savefig(response, format="png")
return response
Hence, you can return the image directly in the HttpResponse.
what about cStringIO?
import pylab
import cStringIO
pylab.plot([3,7,2,1])
output = cStringIO.StringIO()
pylab.savefig('test.png', dpi=75)
pylab.savefig(output, dpi=75)
print output.getvalue() == open('test.png', 'rb').read() # True
There is a recipe in the Matplotlib Cookbook that does exactly this. At its core, it looks like:
def simple(request):
from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure
fig=Figure()
ax=fig.add_subplot(111)
ax.plot(range(10), range(10), '-')
canvas=FigureCanvas(fig)
response=django.http.HttpResponse(content_type='image/png')
canvas.print_png(response)
return response
Put that in your views file, point your URL to it, and you're off and running.
Edit: As noted, this is a simplified version of a recipe in the cookbook. However, it looks like there is a difference between calling print_png and savefig, at least in the initial test that I did. Calling fig.savefig(response, format='png') gave an image with that was larger and had a white background, while the original canvas.print_png(response) gave a slightly smaller image with a grey background. So, I would replace the last few lines above with:
canvas=FigureCanvas(fig)
response=django.http.HttpResponse(content_type='image/png')
fig.savefig(response, format='png')
return response
You still need to have the canvas instantiated, though.
Employ ducktyping and pass a object of your own, in disguise of file object
class MyFile(object):
def __init__(self):
self._data = ""
def write(self, data):
self._data += data
myfile = MyFile()
fig.savefig(myfile)
print myfile._data
you can use myfile = StringIO.StringIO() instead in real code and return data in reponse e.g.
output = StringIO.StringIO()
fig.savefig(output)
contents = output.getvalue()
return HttpResponse(contents , mimetype="image/png")
