Get the value attribute, or if it doesn't exist the text
        content.
        <option value="foo">bar</option> => "foo"
        <option>bar</option> => "bar"
        :param elem: a soup element

def get_option_value(elem):
    """ Get the value attribute, or if it doesn't exist the text
        content.
        <option value="foo">bar</option> => "foo"
        <option>bar</option> => "bar"
        :param elem: a soup element
    """
    value = elem.get("value")
    if value is None:
        value = elem.text.strip()
    if value is None or value == "":
        msg = u"Error parsing value from {}.".format(elem)
        raise ValueError(msg)

    return value