如何用python实现简单的学生选课系统

以下是一个简单的学生选课系统的 Python 代码示例：

class Student:
    def __init__(self, name, id_num):
        self.name = name
        self.id_num = id_num
        self.courses = []

    def add_course(self, course):
        self.courses.append(course)

    def remove_course(self, course):
        self.courses.remove(course)

class Course:
    def __init__(self, name, id_num, professor):
        self.name = name
        self.id_num = id_num
        self.professor = professor
        self.students = []

    def add_student(self, student):
        self.students.append(student)
        student.add_course(self)

    def remove_student(self, student):
        self.students.remove(student)
        student.remove_course(self)

    def list_students(self):
        for student in self.students:
            print(student.name)

class School:
    def __init__(self):
        self.students = []
        self.courses = []

    def add_student(self, name, id_num):
        student = Student(name, id_num)
        self.students.append(student)

    def add_course(self, name, id_num, professor):
        course = Course(name, id_num, professor)
        self.courses.append(course)

    def register_student(self, student_id, course_id):
        student = self.get_student_by_id(student_id)
        course = self.get_course_by_id(course_id)
        course.add_student(student)

    def unregister_student(self, student_id, course_id):
        student = self.get_student_by_id(student_id)
        course = self.get_course_by_id(course_id)
        course.remove_student(student)

    def list_students_in_course(self, course_id):
        course = self.get_course_by_id(course_id)
        course.list_students()

    def get_student_by_id(self, student_id):
        for student in self.students:
            if student.id_num == student_id:
                return student
        return None

    def get_course_by_id(self, course_id):
        for course in self.courses:
            if course.id_num == course_id:
                return course
        return None

# Example usage
school = School()
school.add_student("Alice", 1234)
school.add_student("Bob", 5678)
school.add_course("Math", 1001, "Prof. Smith")
school.add_course("Science", 1002, "Prof. Johnson")
school.register_student(1234, 1001)
school.register_student(5678, 1001)
school.register_student(5678, 1002)
school.list_students_in_course(1001)

这个简单的学生选课系统包括三个类：`Student`，`Course`和`School`。`Student`类表示学生，`Course`类表示课程，`School`类表示学校。在`School`类中，有一些方法可以添加学生和课程，注册学生到课程中，取消学生在课程中的注册，列出某个课程中的所有学生等。