分别定义Person类、Employee类、Student类以及在职研 究生类PartTime_Graduate_Student，并且画出相应的继承层 次图

Person类是一个基类，用于描述一个人的基本信息，如姓名、年龄、性别等。Employee类和Student类都继承自Person类，分别用于描述一个职员和一个学生的信息。PartTime_Graduate_Student类继承自Employee类和Student类，表示一个在职研究生的信息。以下是各个类的定义以及继承关系图：

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

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

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

class PartTime_Graduate_Student(Employee, Student):
    def __init__(self, name, age, gender, company, school):
        Employee.__init__(self, name, age, gender, company)
        Student.__init__(self, name, age, gender, school)

继承关系图：

   +------------+
   |   Person   |
   +-----+------+
         |
         |
   +-----+------+
   |  Student  |
   +-----+------+
         |
         |
   +-----+------+
   |  Employee |
   +-----+------+ 
         |
         |  
   +-----+------+  
   | PartTime  |
   |   Grad.   |
   +-----------+