How to add an empty column to a dataframe?

What's the easiest way to add an empty column to a pandas DataFrame object? The best I've stumbled upon is something like

    df['foo'] = df.apply(lambda _: '', axis=1)

Is there a less perverse method?

If I understand correctly, assignment should fill:

    >>> df = pd.DataFrame({"A": [1,2,3], "B": [2,3,4]})
    >>> df
       A  B
    0  1  2
    1  2  3
    2  3  4
    >>> df["C"] = ""
    >>> df["D"] = np.nan
    >>> df
       A  B C   D
    0  1  2   NaN
    1  2  3   NaN
    2  3  4   NaN

From: stackoverflow.com/q/16327055