title: Pyvista: find out which mesh was picked
body: <p>I add some spheres to my Pyvista plot and try to make them pickable:</p>
  <pre><code>for index, center in enumerate(centers):
      sphere = pv.Sphere(radius=radius, center=center)
      plotter.add_mesh(sphere, color=thisColor, pickable=True)
      plotter.enable_cell_picking(mesh=sphere, callback=makePickCallback(index), show=True, show_message=True, through=False)
  </code></pre>
  <p>I assume that each sphere would get an individual callback, constructed using the following function:</p>
  <pre><code>def makePickCallback(index):
      indexCopy = deepcopy(index)
      return lambda p: print(str(indexCopy) + &quot; &quot; + str(p))
  </code></pre>
  <p>But it seems that all spheres, and every other element in the plot just calls the callback that was constructed in the last iteration of the <code>for</code> loop.</p>
  <p>Now I wonder - <strong>how can I install a different picking callback for each mesh in the scene? Or how can I identify which mesh was clicked?</strong></p>