python设计一个学生管理系统，包括功能：1.添加学生、2.删除学生、3.修改学生信息、4.查询单个学生信息、5.查询所有学生的信息、6.退出系统

好的，下面是一个简单的学生管理系统的 Python 代码实现：

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

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

    def add_student(self, student):
        self.students.append(student)
        print("添加成功！")

    def delete_student(self, id_num):
        for student in self.students:
            if student.id_num == id_num:
                self.students.remove(student)
                print("删除成功！")
                return
        print("该学生不存在！")

    def modify_student(self, id_num):
        for student in self.students:
            if student.id_num == id_num:
                name = input("请输入修改后的姓名：")
                age = input("请输入修改后的年龄：")
                gender = input("请输入修改后的性别：")
                student.name = name if name else student.name
                student.age = age if age else student.age
                student.gender = gender if gender else student.gender
                print("修改成功！")
                return
        print("该学生不存在！")

    def query_student(self, id_num):
        for student in self.students:
            if student.id_num == id_num:
                print(f"姓名：{student.name}，年龄：{student.age}，性别：{student.gender}，学号：{student.id_num}")
                return
        print("该学生不存在！")

    def query_all_students(self):
        for student in self.students:
            print(f"姓名：{student.name}，年龄：{student.age}，性别：{student.gender}，学号：{student.id_num}")

    def exit_system(self):
        print("退出系统！")

if __name__ == "__main__":
    sms = StudentManagementSystem()
    while True:
        print("欢迎使用学生管理系统！")
        print("1.添加学生\n2.删除学生\n3.修改学生信息\n4.查询单个学生信息\n5.查询所有学生的信息\n6.退出系统")
        choice = input("请选择功能：")
        if choice == "1":
            name = input("请输入姓名：")
            age = input("请输入年龄：")
            gender = input("请输入性别：")
            id_num = input("请输入学号：")
            student = Student(name, age, gender, id_num)
            sms.add_student(student)
        elif choice == "2":
            id_num = input("请输入要删除的学生学号：")
            sms.delete_student(id_num)
        elif choice == "3":
            id_num = input("请输入要修改的学生学号：")
            sms.modify_student(id_num)
        elif choice == "4":
            id_num = input("请输入要查询的学生学号：")
            sms.query_student(id_num)
        elif choice == "5":
            sms.query_all_students()
        elif choice == "6":
            sms.exit_system()
            break
        else:
            print("输入有误，请重新输入！")

运行程序后，根据提示选择功能即可。