用python20.创建一个名为Student的类，包含姓名、学号和年级属性。从文件中读取数据并创建Student对象列表。将这些对象按学号排序并将结果写入另一个文件。 21.创建一个名为Book的类，包含书名、作者和价格属性。从文件中读取数据并创建Book对象列表。找出价格最高的书并输出书名和作者。 22.创建一个名为Employee的类，包含名字、工号和薪水属性。从文件中读取数据并创建Employee对象列表。将这些对象按薪水排序并将结果写入另一个文件。 23.创建一个名为Person的类，包含姓名、年龄和性别属性。从文件中读取数据并创建Person对象列表。将这些对象按年龄从大到小排序并将结果写入另一个文件。 创建一个名为Rectangle的类，包含长和宽属性。从文件中读取数据并创建Rectangle对象列表。计算并输出所有矩形对象的周长和面积之和。

好的，我已经了解您的要求了，下面是代码：

20.

class Student:
    def __init__(self, name, student_id, grade):
        self.name = name
        self.student_id = student_id
        self.grade = grade

def read_students(file_name):
    student_list = []
    with open(file_name, 'r') as f:
        lines = f.readlines()
        for line in lines:
            data = line.strip().split(',')
            student_list.append(Student(data[0], data[1], data[2]))
    return student_list

def write_students(student_list, file_name):
    student_list.sort(key=lambda x: x.student_id)
    with open(file_name, 'w') as f:
        for student in student_list:
            f.write(f'{student.name},{student.student_id},{student.grade}\n')

students = read_students('students.txt')
write_students(students, 'sorted_students.txt')

21.

class Book:
    def __init__(self, title, author, price):
        self.title = title
        self.author = author
        self.price = price

def read_books(file_name):
    book_list = []
    with open(file_name, 'r') as f:
        lines = f.readlines()
        for line in lines:
            data = line.strip().split(',')
            book_list.append(Book(data[0], data[1], float(data[2])))
    return book_list

def find_highest_priced_book(book_list):
    highest_priced_book = book_list[0]
    for book in book_list:
        if book.price > highest_priced_book.price:
            highest_priced_book = book
    return highest_priced_book

books = read_books('books.txt')
highest_priced_book = find_highest_priced_book(books)
print(f'The highest priced book is {highest_priced_book.title} by {highest_priced_book.author}.')

22.

class Employee:
    def __init__(self, name, employee_id, salary):
        self.name = name
        self.employee_id = employee_id
        self.salary = salary

def read_employees(file_name):
    employee_list = []
    with open(file_name, 'r') as f:
        lines = f.readlines()
        for line in lines:
            data = line.strip().split(',')
            employee_list.append(Employee(data[0], data[1], int(data[2])))
    return employee_list

def write_employees(employee_list, file_name):
    employee_list.sort(key=lambda x: x.salary)
    with open(file_name, 'w') as f:
        for employee in employee_list:
            f.write(f'{employee.name},{employee.employee_id},{employee.salary}\n')

employees = read_employees('employees.txt')
write_employees(employees, 'sorted_employees.txt')

23.

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

def read_people(file_name):
    person_list = []
    with open(file_name, 'r') as f:
        lines = f.readlines()
        for line in lines:
            data = line.strip().split(',')
            person_list.append(Person(data[0], int(data[1]), data[2]))
    return person_list

def write_people(person_list, file_name):
    person_list.sort(key=lambda x: x.age, reverse=True)
    with open(file_name, 'w') as f:
        for person in person_list:
            f.write(f'{person.name},{person.age},{person.gender}\n')

people = read_people('people.txt')
write_people(people, 'sorted_people.txt')

24.

class Rectangle:
    def __init__(self, length, width):
        self.length = length
        self.width = width

    def area(self):
        return self.length * self.width

    def perimeter(self):
        return 2 * (self.length + self.width)

def read_rectangles(file_name):
    rectangle_list = []
    with open(file_name, 'r') as f:
        lines = f.readlines()
        for line in lines:
            data = line.strip().split(',')
            rectangle_list.append(Rectangle(int(data[0]), int(data[1])))
    return rectangle_list

def calculate_total_area_and_perimeter(rectangle_list):
    total_area = 0
    total_perimeter = 0
    for rectangle in rectangle_list:
        total_area += rectangle.area()
        total_perimeter += rectangle.perimeter()
    return total_area, total_perimeter

rectangles = read_rectangles('rectangles.txt')
total_area, total_perimeter = calculate_total_area_and_perimeter(rectangles)
print(f'Total area: {total_area} sq. units')
print(f'Total perimeter: {total_perimeter} units')