python 定义一个Person类有name, age, sex的公有成员变量，以及一个showinfor（）的方法对该类的三个属性进行打印。再定义一个Teacher类，该类继承Person类，并且额外新增一个department的公有成员变量，也对Teacher类定义一个showinfor（）的方法对该类的四个属性进行打印。再定义一个Student类，该类继承Person类，并且额外新增一个marks的公有成员变量，也对Student类定义一个showinfor（）的方法对该类的四个属性进行打印。

这是一个计算机编程问题，我可以回答。以下是Python代码实现：

class Person:
    def __init__(self, name, age, sex):
        self.name = name
        self.age = age
        self.sex = sex
        
    def showinfor(self):
        print(f"Name: {self.name}, Age: {self.age}, Sex: {self.sex}")
        
class Teacher(Person):
    def __init__(self, name, age, sex, department):
        super().__init__(name, age, sex)
        self.department = department
        
    def showinfor(self):
        print(f"Name: {self.name}, Age: {self.age}, Sex: {self.sex}, Department: {self.department}")

class Student(Person):
    def __init__(self, name, age, sex, marks):
        super().__init__(name, age, sex)
        self.marks = marks
        
    def showinfor(self):
        print(f"Name: {self.name}, Age: {self.age}, Sex: {self.sex}, Marks: {self.marks}")

可以使用以下代码测试：

person1 = Person("Alice", 20, "Female")
person1.showinfor()

teacher1 = Teacher("Bob", 30, "Male", "Computer Science")
teacher1.showinfor()

student1 = Student("Charlie", 18, "Male", 90)
student1.showinfor()

输出结果：

Name: Alice, Age: 20, Sex: Female
Name: Bob, Age: 30, Sex: Male, Department: Computer Science
Name: Charlie, Age: 18, Sex: Male, Marks: 90