Unusual behaviour of pick_event in a matplotlib

Question

When fig.canvas.draw() is used in onclick function, it doesn't wait for onclick event, and it comes out of the function. How to make it work continuously, so that label can be displayed every time when clicked on the pie chart.

import matplotlib.pyplot as plt
labels = ['Beans', 'Squash', 'Corn']
def main():
    # Make an example pie plot
    fig = plt.figure()
    ax = fig.add_subplot(111)

    #labels = ['Beans', 'Squash', 'Corn']
    wedges, plt_labels = ax.pie([20, 40, 60], labels=labels)
    ax.axis('equal')

    make_picker(fig, wedges)
    plt.show()

def make_picker(fig, wedges):

    def onclick(event):
        print event.__class__
        wedge = event.artist
        label = wedge.get_label()
        print label
        fig.canvas.figure.clf() 
        ax=fig.add_subplot(111)
        wedges, plt_labels = ax.pie([50, 100, 60],labels=labels)
        fig.canvas.draw()

    # Make wedges selectable
    for wedge in wedges:
        wedge.set_picker(True)

    fig.canvas.mpl_connect('pick_event', onclick)

if __name__ == '__main__':
    main()

Answer 1

Your problem is in the onclick function.

def onclick(event):
    print event.__class__
    wedge = event.artist
    label = wedge.get_label()
    print label
    fig.canvas.figure.clf() 
    ax=fig.add_subplot(111)
    wedges, plt_labels = ax.pie([50, 100, 60],labels=labels)
    fig.canvas.draw()

Here you are creating new wedges (which overwrite your old wedges instances) and you are not setting them to be pickable. A quick patch for this is to change onclick to:

def onclick(event):
    print event.__class__
    wedge = event.artist
    label = wedge.get_label()
    print label
    fig.canvas.figure.clf()
    ax=fig.add_subplot(111)
    wedges, plt_labels = ax.pie([50, 100, 60],labels=labels)
    fig.canvas.draw()
    for wedge in wedges:
        wedge.set_picker(True)