Merging dataframes on index with pandas

I have two dataframes and each one has two index columns. I would like to merge them. For example, the first dataframe is the following:

                       V1

    A      1/1/2012    12
           2/1/2012    14
    B      1/1/2012    15
           2/1/2012    8
    C      1/1/2012    17
           2/1/2012    9

The second dataframe is the following:

                       V2

    A      1/1/2012    15
           3/1/2012    21             
    B      1/1/2012    24
           2/1/2012    9
    D      1/1/2012    7
           2/1/2012    16

and as result I would like to get the following:

                       V1   V2

    A      1/1/2012    12   15
           2/1/2012    14   N/A
           3/1/2012    N/A  21           
    B      1/1/2012    15   24
           2/1/2012    8    9
    C      1/1/2012    7    N/A
           2/1/2012    16   N/A
    D      1/1/2012    N/A  7
           2/1/2012    N/A  16

I have tried a few versions using the pd.merge and .join methods, but nothing seems to work. Do you have any suggestions?

You should be able to use join, which joins on the index as default. Given your desired result, you must use outer as the join type.

    >>> df1.join(df2, how='outer')
                V1  V2
    A 1/1/2012  12  15
      2/1/2012  14 NaN
      3/1/2012 NaN  21
    B 1/1/2012  15  24
      2/1/2012   8   9
    C 1/1/2012  17 NaN
      2/1/2012   9 NaN
    D 1/1/2012 NaN   7
      2/1/2012 NaN  16

Signature: _.join(other, on=None, how='left', lsuffix='', rsuffix='', sort=False) Docstring: Join columns with other DataFrame either on index or on a key column. Efficiently Join multiple DataFrame objects by index at once by passing a list.

From: stackoverflow.com/q/36538780