In the Docstring for the Merge method, the example provided:

merge(A, B, left_on='lkey', right_on='rkey', how='outer') 

returns a sorted DataFrame. Thus, we need to either add a sort=True kwarg to the above code or replace the purported output with the actual (unsorted) output:

 lkey value_x rkey value_y 0 foo 1 foo 5 1 foo 4 foo 5 2 bar 2 bar 6 3 bar 2 bar 8 4 baz 3 NaN NaN 5 NaN NaN qux 7