title: matplotlib.widgets Button doesn't work inside a class
body: <p>I took the example for a <a href="http://matplotlib.org/examples/widgets/slider_demo.html" rel="nofollow noreferrer">slider widget</a> , and tried to plug it into a class. The sliders work properly, but for some reason the Button and RadioButtons does not react when the method is inside a class:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  from matplotlib.widgets import Slider, Button, RadioButtons
  class test(object):
      def __init__(self):
  
          fig, ax = plt.subplots()
          plt.subplots_adjust(left=0.25, bottom=0.25)
          t = np.arange(0.0, 1.0, 0.001)
          a0 = 5
          f0 = 3
          s = a0*np.sin(2*np.pi*f0*t)
          l, = plt.plot(t, s, lw=2, color='red')
          plt.axis([0, 1, -10, 10])
  
          axcolor = 'lightgoldenrodyellow'
          axfreq = plt.axes([0.25, 0.1, 0.65, 0.03], facecolor=axcolor)
          axamp = plt.axes([0.25, 0.15, 0.65, 0.03], facecolor=axcolor)
  
          sfreq = Slider(axfreq, 'Freq', 0.1, 30.0, valinit=f0)
          samp = Slider(axamp, 'Amp', 0.1, 10.0, valinit=a0)
  
  
          def update(val):
              amp = samp.val
              freq = sfreq.val
              l.set_ydata(amp*np.sin(2*np.pi*freq*t))
              fig.canvas.draw_idle()
          sfreq.on_changed(update)
          samp.on_changed(update)
  
          resetax = plt.axes([0.8, 0.025, 0.1, 0.04])
          button = Button(resetax, 'Reset', color=axcolor, hovercolor='0.975')
  
          def reset(event):
              sfreq.reset()
              samp.reset()
          button.on_clicked(reset)
  
          rax = plt.axes([0.025, 0.5, 0.15, 0.15], facecolor=axcolor)
          radio = RadioButtons(rax, ('red', 'blue', 'green'), active=0)
  
  
          def colorfunc(label):
              l.set_color(label)
              fig.canvas.draw_idle()
          radio.on_clicked(colorfunc)
  
          plt.show()
  </code></pre>
  
  <p>If I try now to use this class the Button and RadioButton are freezed..anyone encountered this?</p>