title: python: plot with a repeated legend
body: <p>I have 3 files to plot (pos_Felix, pos_Iando, pos_Fabiotto). For some reason I have to put them together in a unique file. A reproducible code follows:</p>
  
  <pre><code>from matplotlib import pylab
  import numpy
  
  pos_Felix = numpy.array([ [  3.05150657e-01,  -7.33839341e-01],
                          [  3.24785115e-01,  -5.70699171e-01],
                          [ -1.90952119e-02,  -9.31596157e-01],
                          [  1.01292710e+00,  -3.75807265e-01],
                          [  3.32793456e-01,  -6.54133767e-01]])
  
  pos_Iando = numpy.array([ [  3.41211808e-04,  -1.43754261e-02],
                          [ -1.18384581e-01,  -4.84193704e-01]])
  
  pos_Fabiotto = numpy.array([ [ -4.63776141e-01,   1.62560557e+00]])
  
  pos_all = numpy.concatenate([pos_Felix,pos_Iando,pos_Fabiotto],axis=0)
  
  
  myColors = ['green']*pos_Felix.shape[0] + ['red']*(pos_Iando.shape[0]+pos_Fabiotto.shape[0])
  
  myShapes    =   ['.']*pos_Felix.shape[0]     + ['^']*pos_Iando.shape[0]       + ['*']*pos_Fabiotto.shape[0]
  myLabels    =   ['Felix']*pos_Felix.shape[0] + ['Iando']*pos_Iando.shape[0]   + ['Fabiotto']*pos_Fabiotto.shape[0]
  
  
  
  pylab.figure()
  pylab.title("Multi Dimensional Scaling")
  pylab.xlabel("X")
  pylab.ylabel("Y")
  for i in range(pos_all.shape[0]):
      pylab.plot(pos_all[i,0],pos_all[i,1],myShapes[i], color=myColors[i], label=myLabels[i])
  pylab.legend(loc="upper left")
  
  pylab.show()
  </code></pre>
  
  <p>In a few words, I have to plot a sequence of points (I am sure that the "for" construct is not the best one, but at least it works so far), each one with a colour, each one belonging to a category ("Felix", "Iando" and "Fabiotto"), each one with its marker. The graph is ok, except the legend. It is of length 8 instead of 3. I get the following image (in red what I would like to remove):</p>
  
  <p><a href="https://i.stack.imgur.com/l4L7j.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/l4L7j.png" alt="enter image description here"></a></p>
  
  <p>I am sure there is a quick way to solve my issue... but i do not know which one!
  ps= I know I could create a list of legends with only 3 elements in the right places and "None" for the others, but in my real case I have very long lists and i need an automated procedure.</p>