>>> func = to_python({'one': 'n in 1,11', 'few': 'n in 3..10,13..19'})
    >>> func(11)
    'one'
    >>> func(15)
    'few'

    :param rule: the rules as list or dict, or a `PluralRule` object
    :raise RuleError: if the expression is malformed
    )