def mean_df(objects):
    """Basic calculation of mean (average) of a list of DataFrames.

    Parameters
    ----------
    objects : list of pandas.DataFrame
        the DataFrames to calculate the mean (NB: technically, these don't
        have to be DataFrames. They must be closed on the `sum` operation
        and over division by a float.

    Returns
    -------
    pandas.DataFrame :
        the mean of each element in the DataFrame
    """
    return sum(objects) / float(len(objects))