title: Merging two dataframes with same column names but different number of columns in pandas
body: <p>I have two pandas dataframes</p>
  
  <pre><code>df1 = DataFrame([[0,123,321],[0,1543,432]], columns=['A', 'B','C'])
  df2 = DataFrame([[1,124],[1,1544]], columns=['A', 'C'])
  </code></pre>
  
  <p>I want to merge these so that the new dataframe would look like below</p>
  
  <pre><code>A     |    B      |   C
  0         123        321
  0         1543       432
  1         null       124
  1         null       1544
  </code></pre>
  
  <p>I have tried using append and concat but nothing seems to work. Any help would be much appreciated.</p>