def format_cols_2digit(df, skip_last_col=True):
    """Formats a dataframes columns so that numbers are always two-digits (padded with 0)

    Parameters
    ----------
    df : pandas DataFrame
        Input DataFrame.
    skip_last_col : bool
        A special case, where the very last column contains text, rather than a number, and should be excluded.

    Returns
    -------
    reformatted_cols : list
        The DataFrame columns, reformatted with padded 0 to make 2 digits.

    """
    if skip_last_col:
        # reformat the columns to be padded stringnumbers. (exclude the last "Contains_Data")
        reformatted_cols = ["%02d" % col for col in df.columns[:-1]]
        # add last column back to list
        reformatted_cols.append(df.columns[-1])
    else:
        # reformat the columns to be padded stringnumbers. (exclude the last "Contains_Data")
        reformatted_cols = ["%02d" % col for col in df.columns]

    return reformatted_cols