'Compares student submitted checkbox/radiobutton answers against
the correct answers. Returns True or False.
True if all of the correct choices are selected and no incorrect
choices are selected.'

def _check_student_choices(self, choices):

    student_choices = set(choices)
    required_selected = (len((self.correct_choices - student_choices)) == 0)
    no_extra_selected = (len((student_choices - self.correct_choices)) == 0)
    correct = (required_selected and no_extra_selected)
    return correct
