'Given the staff answer as a string, find its float value.
Use `evaluator` for this, but for backward compatability, try the
built-in method `complex` (which used to be the standard).'

def get_staff_ans(self, answer):

    try:
        correct_ans = complex(answer)
    except ValueError:
        try:
            correct_ans = evaluator({}, {}, answer)
        except Exception:
            log.debug("Content    error--answer    '%s'    is    not    a    valid    number", answer)
            _ = self.capa_system.i18n.ugettext
            raise StudentInputError(_('There    was    a    problem    with    the    staff    answer    to    this    problem.'))
    return correct_ans
