title: How to create a live updating matplotlib graph in gtk3
body: <p>I wanted to put my live plotting app into a nice gtk3 programm and so far I got this but it doesn't show a window. What am I missing? Thanks in advance!</p>
  
  <pre><code>import serial
  import numpy as np
  
  from matplotlib.figure import Figure
  from matplotlib.backends.backend_gtk3cairo import FigureCanvasGTK3Cairo as FigureCanvas
  from gi.repository import Gtk
  
  class MyWindow(Gtk.ApplicationWindow):
      def __init__(self):
  
      Gtk.Window.__init__(self, title="Toolbar Example")
          self.set_size_request(700, 500)
      self.box = Gtk.Box(spacing=6, orientation=Gtk.Orientation.VERTICAL)
      self.add(self.box)
  
      fig = Figure()
      ax = fig.add_subplot(111)
      ax.set_xlim(0, 50)
      ax.set_ylim(0, 20)
  
      ydata = [0] * 50
      line, = ax.plot(ydata, label='ydata')
      ax.legend()
  
      f = FigureCanvas(fig)
      self.box.pack_start(f, True, True, 0)
  
      while True:
          ydata.append(10)
          line.set_data(np.arange(len(ydata)), ydata)
          f.draw()
  
  
  win = MyWindow()
  win.connect("delete-event", Gtk.main_quit)
  win.show_all()
  Gtk.main()
  </code></pre>