Rename a set of columns in a DataFrame
    Parameters:
    df - DataFrame
        DataFrame to operate on
    col_names - list of strings
        names of columns to change
    new_col_names - list of strings
        new names for old columns (order should be same as col_names)

def cols_rename(df,col_names, new_col_names):
    """ Rename a set of columns in a DataFrame
    Parameters:
    df - DataFrame
        DataFrame to operate on
    col_names - list of strings
        names of columns to change
    new_col_names - list of strings
        new names for old columns (order should be same as col_names)
    """
    assert len(col_names) == len(new_col_names)
    for old_name,new_name in zip(col_names,new_col_names):
        col_rename(df,old_name,new_name)