title: Pyplot: show only first 3 lines in legend
body: <p>I'm running a simulation 200 times and plotting the 3 output lists as 3 lines with high transparency. This allows me to show variance between simulations.</p>
  
  <p>The problem is that my legend shows 3x200 items instead of 3 items. How do I get it to show the legend for each line once?</p>
  
  <pre><code>for simulation in range(200):  
      plt.plot(num_s_nodes, label="susceptible", color="blue", alpha=0.02)  
      plt.plot(num_r_nodes, label="recovered", color="green", alpha=0.02)
      plt.plot(num_i_nodes, label="infected", color="red", alpha=0.02)
  plt.legend()  
  plt.show()
  </code></pre>