[SciPy-user] Solved-ish: matplotlib, Tkinter and multi-threaded web applications

[zunzun at zunzun.com]

On Sun, Oct 14, 2007 at 07:23:19PM -0500, Robert Kern wrote:
> 
> Please show us the code that you used on the matplotlib list.

timesRequested = 0

    def getBufferForPNG(self):
        global timesRequested # use the global variable defined at the top of the module

        # make a buffer to hold our data
        buffer = StringIO.StringIO()

        # pylab uses Tkinter, so this must be the top-level thread calling Tk.
        # calling pylab.close() here forces pylab to create a new top-level thread
        pylab.close()

        # tell matplotlib to use the 'Anti-Grain Geometry' toolkit
        matplotlib.use('Agg')

        canvas = pylab.get_current_fig_manager().canvas

        # quick simple plot
        pylab.plot([1+timesRequested, 2+timesRequested, 3+timesRequested],[40+timesRequested, 
50+timesRequested, 60+timesRequested])

        timesRequested += 1 # this is only to give a different graph with each refresh

        canvas.draw()
        imageSize = canvas.get_width_height()
        imageRgb = canvas.tostring_rgb()
        pilImage = PIL.Image.fromstring("RGB", imageSize, imageRgb)

        pilImage.save(buffer, "PNG") # <-- we will be sending the browser a "PNG file"
        
        pylab.close() # close again to be sure of Tk threading

        return buffer