python - Is it possible to add several columns at once to a pandas DataFrame?

Question

If I want to create a new DataFrame with several columns, I can add all the columns at once -- for example, as follows:

data = {'col_1': [0, 1, 2, 3],
        'col_2': [4, 5, 6, 7]}
df = pd.DataFrame(data)

But now suppose farther down the road I want to add a set of additional columns to this DataFrame. Is there a way to add them all simultaneously, as in

additional_data = {'col_3': [8, 9, 10, 11],
                   'col_4': [12, 13, 14, 15]}
#Below is a made-up function of the kind I desire.
df.add_data(additional_data)

I'm aware I could do this:

for key, value in additional_data.iteritems():
    df[key] = value

Or this:

df2 = pd.DataFrame(additional_data, index=df.index)
df = pd.merge(df, df2, on=df.index)

I was just hoping for something cleaner. If I'm stuck with these two options, which is preferred?

Answer 1

Pandas has assign method since 0.16.0. You could use it on dataframes like

In [1506]: df1.assign(**df2)
Out[1506]:
   col_1  col_2  col_3  col_4
0      0      4      8     12
1      1      5      9     13
2      2      6     10     14
3      3      7     11     15

or, you could directly use the dictionary like

In [1507]: df1.assign(**additional_data)
Out[1507]:
   col_1  col_2  col_3  col_4
0      0      4      8     12
1      1      5      9     13
2      2      6     10     14
3      3      7     11     15