### December 2010 ###

### Question 3 ###

class BadTypeException(AttributeError):

    pass

def list_to_lower(str_list):
    """
    Return a new list of the elements in str_list after they have been
    turned to lowercase strings. str_list should be a list of strings, otherwise
    a BadTypeException is raised with the error message: 'Non-string object
    found.'
    """

    new_str_list = []

    for element in str_list:
        try:
            new_str_list.append(element.lower())
        except:
            raise BadTypeException, 'Non-string object found.'

    return new_str_list