title: Python scattered chart legend
body: <p>I'm plotting a scattered chart which look like this :</p>
  
  <pre><code>from pylab import *
  
  n = 1024
  X = np.random.normal(0,1,n)
  Y = np.random.normal(0,1,n)
  T = np.arctan2(Y,X)
  
  axes([0.025,0.025,0.95,0.95])
  scatter(X,Y, s=75, c=T, alpha=.5)
  
  xlim(-1.5,1.5), xticks([])
  ylim(-1.5,1.5), yticks([])
  # savefig('../figures/scatter_ex.png',dpi=48)
  show()
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/UNhY5.png" alt="enter image description here"></p>
  
  <p>I would like to add a legend to explain the color scale :</p>
  
  <p>Like yellow is 0 red is 10 etc...</p>
  
  <p>I cannot find a way to do it , it works for imshow like this one :</p>
  
  <pre><code>from pylab import *
  
  def f(x,y): return (1-x/2+x**5+y**3)*np.exp(-x**2-y**2)
  
  n = 10
  x = np.linspace(-3,3,3.5*n)
  y = np.linspace(-3,3,3.0*n)
  X,Y = np.meshgrid(x,y)
  Z = f(X,Y)
  
  axes([0.025,0.025,0.95,0.95])
  imshow(Z,interpolation='nearest', cmap='bone', origin='lower')
  colorbar(shrink=.92)
  
  xticks([]), yticks([])
  # savefig('../figures/imshow_ex.png', dpi=48)
  show()
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/k8NSS.png" alt="enter image description here"></p>
  
  <p>BUt I cannot find a way to add it on scattered charts.</p>
  
  <p>DOes anyone already had to deal with this issue ?</p>
  
  <p>Thanks for your help.</p>