Coerces a list of columns to categorical
    Parameters:
    df - DataFrame
        DataFrame to operate on
    col_list - list of strings
        names of columns to coerce
    dest - bool, default False
        Whether to apply the result to the DataFrame or return it.
        True is apply, False is return.

def cols_to_cat(df, col_list,dest = False):
    """ Coerces a list of columns to categorical
    Parameters:
    df - DataFrame
        DataFrame to operate on
    col_list - list of strings
        names of columns to coerce
    dest - bool, default False
        Whether to apply the result to the DataFrame or return it.
        True is apply, False is return.
    """
    # Convert a list of columns to categorical
    if not dest:
        return _pd.DataFrame({col_name:col_to_cat(df,col_name) for col_name in col_list})
    for col_name in col_list:
        col_to_cat(df,col_name,dest)