How to get the label on bar plot/stacked bar plot in matplotlib?

Question

I have a very simple stacked matplotlib bar plot embedded in PyQt Canvas. I am trying to get the corresponding label of the bar area (rectangle) based on the click. But I would always be getting _nolegend_ when I try to print the information from the event. Ideally I would like to see the corresponding label on the bar attached in the code.

For example when you click the gray bar it should print a2

import sys
import matplotlib.pyplot as plt

from PyQt4 import QtGui
from matplotlib.figure import Figure
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas


def on_pick(event):
    print event.artist.get_label()

def main():

    app = QtGui.QApplication(sys.argv)

    w = QtGui.QWidget()
    w.resize(640, 480)
    w.setWindowTitle('Pick Test')

    fig = Figure((10.0, 5.0), dpi=100)
    canvas = FigureCanvas(fig)
    canvas.setParent(w)

    axes = fig.add_subplot(111)

    # bind the pick event for canvas
    fig.canvas.mpl_connect('pick_event', on_pick)

    p1 = axes.bar(1,6,picker=2,label='a1')
    p2 = axes.bar(1,2, bottom=6,color='gray',picker=1,label='a2')

    axes.set_ylim(0,10)
    axes.set_xlim(0,5)

    w.show()

    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

Answer 1

This gets a little tricky because bar is a complex plot object that is really composed of multiple components.

You can use get_legend_handles_labels to get all the artists and labels for the axes. Then you can look so see which group your current artist belongs to.

So your callback may look something like this.

def on_pick(event)
    rect = event.artist

    # Get the artists and the labels
    handles,labels = rect.axes.get_legend_handles_labels()

    # Search for your current artist within all plot groups
    label = [label for h,label in zip(handles, labels) if rect in h.get_children()]

    # Should only be one entry but just double check
    if len(label) == 1:
        label = label[0]
    else:
        label = None

    print label