Question

I have a visualizer for network traffic in Python. It uses Twisted for networking and calls run() it also has matplotlib for plotting and calls show(). Neither of these functions seem to return yet I need to call both of them to start the networking, then show the plot and ultimately update the plot as things happen on the network. Any solutions? Do I need threads?

Answer 1

matplotlib is a layer on top of some GUI toolkit. Which GUI toolkit depends a bit – on per-user configuration, on site-wide configuration, on the particulars of the matplotlib code you have.

Twisted has specific support for integrating with some GUI toolkits. So, for example, you can run matplotlib with its Gtk backend and use Twisted’s Gtk integration and then everything will play nicely together.

Here’s a 5 minute hack I threw together, based on what I know about integrating the various mainloops, and on a little bit of inspection of the matplotlib source code:

if __name__ == '__main__':
    from mpl import main
    raise SystemExit(main())

from matplotlib import use
use('GTK')
from matplotlib import pyplot

from matplotlib.backends import backend_gtk

from twisted.internet import gtk2reactor
gtk2reactor.install()

from twisted.internet import reactor, task

class TwistedGtkShow(backend_gtk.Show):
    running = False
    def mainloop(self):
        if not self.running:
            self.running = True
            reactor.run()

def main():
    pyplot.plot([1,2,3,4])
    pyplot.ylabel('some numbers')

    def proof():
        print 'Twisted!'
    task.LoopingCall(proof).start(3)

    TwistedGtkShow()()

Notice:

• This is in a file named mpl.py (hence the mpl import up top)
• I forced matplotlib to use Gtk with the use('GTK') call before importing pyplot
• I forced Twisted to use Gtk with the gtk2reactor.install() call before importing reactor
• I replaced the call to pyplot.show() with a call to my own Show subclass with a mainloop method starts the Gtk mainloop and the Twisted mainloop (both via reactor.run())

This example seems to work fairly well. I haven’t explored this very much, so if there are problems that only crop up under more advanced usage, I don’t know about them.