title: TypeError: 'PathCollection' object is not iterable when adding second legend to plot
body: <p>I am making a scatter plot from three separate dataframes and plotting the points as well as the best fit lines.  I can accomplish this using this code:</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  import matplotlib.pyplot as plt
  
  fig=plt.figure()
  ax1=fig.add_subplot(111)
  ax2=fig.add_subplot(111)
  ax3=fig.add_subplot(111)
  
  #create scatter plots from the dataframes
  ax1.scatter(ex_x, ex_y, s=10, c='r', label='Fire Exclusion')
  ax2.scatter(one_x,one_y, c='b', marker='s',label='One Fire')
  ax3.scatter(two_x, two_y, s=10, c='g', marker='^', label='Two Fires')
  
  #plot lines of best fit
  ax1.plot(ex_x,ex_results.predict(), color = 'r',label = 'Linear (Fire Exclusion)')
  ax2.plot(one_x,one_results.predict(), color = 'b',label = 'Linear (One Fire)')
  ax3.plot(two_x,two_results.predict(), color = 'g',label = 'Linear (Two Fires)')
  
  #add legend and axis labels
  plt.xlabel('NDVI 2004/07/27')
  plt.ylabel('NDVI 2005/07/14')
  plt.title('NDVI in 2004 vs. 2005')
  plt.legend(loc='center left', bbox_to_anchor=(1, 0.5), scatterpoints=1)
  </code></pre>
  
  <p>which gives me:</p>
  
  <p><a href="https://i.stack.imgur.com/Knkn2.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Knkn2.png" alt="enter image description here"></a></p>
  
  <p>Now I want to add a second legend which will display the r2 for each line.  I am attempting to do that like this:</p>
  
  <pre><code>fig=plt.figure()
  ax1=fig.add_subplot(111)
  ax2=fig.add_subplot(111)
  ax3=fig.add_subplot(111)
  
  scat1,=ax1.scatter(ex_x, ex_y, s=10, c='r', label='Fire Exclusion')
  scat2,=ax2.scatter(one_x,one_y, c='b', marker='s',label='One Fire')
  scat3,=ax3.scatter(two_x, two_y, s=10, c='g', marker='^', label='Two Fires')
  
  lin1,=ax1.plot(ex_x,ex_results.predict(), color = 'r',label = 'Linear (Fire Exclusion)')
  lin2,=ax2.plot(one_x,one_results.predict(), color = 'b',label = 'Linear (One Fire)')
  lin3,=ax3.plot(two_x,two_results.predict(), color = 'g',label = 'Linear (Two Fires)')
  
  l1 = plt.legend([scat1, scat2,scat3,lin1,lin2,lin3], ["Fire Exclusion", "One Fire", "Two Fires", "Linear (Fire Exclusion)", "Linear (One Fire)", "Linear (Two Fires)"], loc='upper left', scatterpoints=1)
  
  #get r2 from regression results
  r2ex=ex_results.rsquared
  r2one=one_results.rsquared
  r2two=two_results.rsquared
  
  plt.legend([r2ex, r2one, r2two], ['R2 (Fire Exclusion)', 'R2 (One Fire)', 'R2 (Two Fires)'], loc='lower right')
  
  plt.gca().add_artist(l1)
  plt.xlabel('NDVI 2004/07/27')
  plt.ylabel('NDVI 2005/07/14')
  plt.title('NDVI in 2004 vs. 2005')
  </code></pre>
  
  <p>but this returns:</p>
  
  <pre><code>Traceback (most recent call last):
  
    File "&lt;ipython-input-32-b6277bf27ded&gt;", line 1, in &lt;module&gt;
      runfile('E:/prelim_codes/Fire.py', wdir='E:/prelim_codes')
  
    File "C:\Users\Stefano\Anaconda2_2\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 714, in runfile
      execfile(filename, namespace)
  
    File "C:\Users\Stefano\Anaconda2_2\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 74, in execfile
      exec(compile(scripttext, filename, 'exec'), glob, loc)
  
    File "E:/prelim_codes/Fire.py", line 539, in &lt;module&gt;
      scat1,=ax1.scatter(ex_x, ex_y, s=10, c='r', label='Fire Exclusion')
  
  TypeError: 'PathCollection' object is not iterable
  </code></pre>