title: Matplotlib: how to show legend for bar chart and line on 2 separate axes?
body: <p>I am plotting a bar chart on the left axis and a line chart on the right axis. How can I show the legend for both in the same legend box?</p>
  
  <p>With the code below, I get two separate legend boxes; also, I need to specify the location of the second legend manually, with lots of trial-and-error, otherwise it overlaps the first one.</p>
  
  <pre><code>import pandas as pd
  import matplotlib.pyplot as plt
  import matplotlib
  
  df=pd.DataFrame()
  df["bar"]=[40,35,50,45]
  df["line"]=[.5,.3,.2,.6]
  
  fig,ax=plt.subplots(2)
  
  l1 = ax[0].bar(df.index, df["bar"], label='my bar chart (left axis)', color='royalblue', width = 0.55)
  ax0b=ax[0].twinx()
  l2 = ax0b.plot(df.index,  df['line'], label='my line (right axis)',color='tomato',marker='.', ls='dashed')
  
  ax[0].legend(loc='upper left', fancybox=True, title='My title')
  ax0b.legend(bbox_to_anchor=(0.155,0.8), loc=1)    
  plt.show()
  </code></pre>
  
  <p>If I had two lines on two different axes, instead of a bar chart and a line chart, I'd do:</p>
  
  <pre><code>myl=l1+l2
  labs=[l.get_label() for l in myl]
  ax[0].legend(myl, labs, loc='upper left')
  </code></pre>
  
  <p>But this doesn't work in my case. I get:</p>
  
  <pre><code>myl=l1+l2
  TypeError: can only concatenate tuple (not "list") to tuple
  </code></pre>
  
  <p>which I imagine must be because bar() and plot() return two different objects which cannot be concatenated.</p>