Person人类有姓名、性别和年龄属性，有吃饭和行走的方法；Student学生类是人类中的一种，学生类特有分数属性和学习、考试方法；Teacher老师类也是人类中的一种，老师类特有的成员有工资属性和讲课方法；Assistant助教既是学生类中的一种，也是老师类中的一种。

请问怎么设计这四种类的关系呢？

这四种类可以使用继承关系进行设计。即，Student和Teacher可以继承Person类的属性和方法，而Assistant则可以同时继承学生和老师的属性和方法。举例来说：

class Person:
def __init__(self, name, gender, age):
self.name = name
self.gender = gender
self.age = age

def eat(self):
print("Person is eating.")

def walk(self):
print("Person is walking.")

class Student(Person):
def __init__(self, name, gender, age, score):
super().__init__(name, gender, age)
self.score = score

def study(self):
print("Student is studying.")

def exam(self):
print("Student is taking an exam.")

class Teacher(Person):
def __init__(self, name, gender, age, salary):
super().__init__(name, gender, age)
self.salary = salary

def lecture(self):
print("Teacher is giving a lecture.")

class Assistant(Student, Teacher):
def __init__(self, name, gender, age, score, salary):
Student.__init__(self, name, gender, age, score)
Teacher.__init__(self, name, gender, age, salary)

def grade(self):
print("Assistant is grading papers.")

# 实例化
person = Person("Tom", "male", 28)
person.eat()
person.walk()

stu = Student("Li", "female", 20, 100)
stu.eat()
stu.walk()
stu.study()
stu.exam()

tea = Teacher("Wang", "male", 35, 10000)
tea.eat()
tea.walk()
tea.lecture()

asst = Assistant("Zhang", "female", 21, 99, 5000)
asst.eat()
asst.walk()
asst.study()
asst.exam()
asst.lecture()
asst.grade()