Using Matplotlib's pick event properly

There are a number of ways to handle this. I've modified your code to try to show two possible ways (so it has extraneous code though matter which way you'd like to handle it).

Generally, I think you'd only attach a single pick_event handler, and that handler would need to determine which object was hit. The code below works that way with the on_pick function capturing your disks, and patches, and then returning a function to tell which figure was clicked.

If you wanted to stick with attaching multiple pick_event handlers, you could do that by tweaking the Disk.onpick as I have below to determine if the pick event was relevant to this disk (each disk will get every pick event). You'll note that the Disk class saves off its patch in self.mypatch for this to work. If you wanted to do it this way, discard all the changes I've made to main, and uncomment the two lines in Disk.mpl_patch.

import matplotlib as mpl
import matplotlib.pyplot as plt 
import numpy as np


class Disk:


    def __init__(self, center, radius, myid = None, figure=None, axes_object=None):
        """ 
        @ARGS
        CENTER : Tuple of floats
        RADIUS : Float
        """
        self.center = center
        self.radius = radius
        self.fig    = figure
        self.ax     = axes_object
        self.myid   = myid
        self.mypatch = None


    def onpick(self,event):
        if event.artist == self.mypatch:
            print "You picked the disk ", self.myid, "  with Center: ", self.center, " and Radius:", self.radius


    def mpl_patch(self, diskcolor= 'orange' ):
        """ Return a Matplotlib patch of the object
        """
        self.mypatch = mpl.patches.Circle( self.center, self.radius, facecolor = diskcolor, picker=1 )

        #if self.fig != None:
            #self.fig.canvas.mpl_connect('pick_event', self.onpick) # Activate the object's method

        return self.mypatch

def on_pick(disks, patches):
    def pick_event(event):
        for i, artist in enumerate(patches):
            if event.artist == artist:
                disk = disks[i]
                print "You picked the disk ", disk.myid, "  with Center: ", disk.center, " and Radius:", disk.radius
    return pick_event


def main():

    fig = plt.figure()
    ax = fig.add_subplot(111)
    ax.set_title('click on disks to print out a message')

    disk_list = []
    patches = []

    disk_list.append( Disk( (0,0), 1.0, 1, fig, ax   )   ) 
    patches.append(disk_list[-1].mpl_patch())
    ax.add_patch(patches[-1])

    disk_list.append( Disk( (3,3), 0.5, 2, fig, ax   )   )
    patches.append(disk_list[-1].mpl_patch())
    ax.add_patch(patches[-1])

    disk_list.append( Disk( (4,9), 2.5, 3, fig, ax   )   )
    patches.append(disk_list[-1].mpl_patch()) 
    ax.add_patch(patches[-1])

    pick_handler = on_pick(disk_list, patches)

    fig.canvas.mpl_connect('pick_event', pick_handler) # Activate the object's method

    ax.set_ylim(-2, 10);
    ax.set_xlim(-2, 10);

    plt.show()


if __name__ == "__main__":
    main()