设计一学生信息管理系统，使之能提供以下功能：1、系统以菜单方式工作2、能够完成对学生信息录入（学生信息用文件保存），可不定时地增加学生信息。3、学生信息浏览功能4、学生信息查询功能（1）按学号查询（2）按姓名查询5、学生信息删除与修改(1)输入学号，若该学生存在，删除该学生信息。6、图书信息的修改输入学号，查询该学生，如果存在，则修改该学生信息（不允许修改学号的程序代码

好的，以下是设计的学生信息管理系统：

import os

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

    def __str__(self):
        return f"Name:{self.name}, Age:{self.age}, ID:{self.id_num}"

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

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

    def delete_student(self, id_num):
        for student in self.students:
            if student.id_num == id_num:
                self.students.remove(student)

    def modify_student(self, id_num, name, age):
        for student in self.students:
            if student.id_num == id_num:
                student.name = name
                student.age = age

    def search_by_id(self, id_num):
        for student in self.students:
            if student.id_num == id_num:
                return student

    def search_by_name(self, name):
        results = []
        for student in self.students:
            if student.name == name:
                results.append(student)
        return results

    def display_all(self):
        for student in self.students:
            print(student)

    def save_to_file(self, file_path):
        with open(file_path, "w") as f:
            for student in self.students:
                f.write(f"{student.name},{student.age},{student.id_num}\n")

    def load_from_file(self, file_path):
        if not os.path.exists(file_path):
            return
        with open(file_path, "r") as f:
            lines = f.readlines()
            for line in lines:
                name, age, id_num = line.strip().split(",")
                student = Student(name, int(age), id_num)
                self.add_student(student)

def main():
    manager = StudentManager()
    file_path = "students.txt"
    manager.load_from_file(file_path)
    while True:
        print("1. Add student")
        print("2. Delete student")
        print("3. Modify student")
        print("4. Search by ID")
        print("5. Search by name")
        print("6. Display all")
        print("7. Save to file")
        print("8. Exit")
        choice = input("Please enter your choice: ")
        if choice == "1":
            name = input("Enter name: ")
            age = input("Enter age: ")
            id_num = input("Enter ID number: ")
            student = Student(name, int(age), id_num)
            manager.add_student(student)
        elif choice == "2":
            id_num = input("Enter ID number: ")
            manager.delete_student(id_num)
        elif choice == "3":
            id_num = input("Enter ID number: ")
            name = input("Enter name: ")
            age = input("Enter age: ")
            manager.modify_student(id_num, name, int(age))
        elif choice == "4":
            id_num = input("Enter ID number: ")
            student = manager.search_by_id(id_num)
            if student:
                print(student)
            else:
                print("Student not found")
        elif choice == "5":
            name = input("Enter name: ")
            students = manager.search_by_name(name)
            if students:
                for student in students:
                    print(student)
            else:
                print("Student not found")
        elif choice == "6":
            manager.display_all()
        elif choice == "7":
            manager.save_to_file(file_path)
            print("Data saved to file")
        elif choice == "8":
            print("Goodbye!")
            break
        else:
            print("Invalid choice")

if __name__ == "__main__":
    main()

这个系统使用了面向对象的编程方式，其中Student类表示一个学生，StudentManager类表示学生信息管理器。系统使用菜单方式工作，可以完成对学生信息的录入、浏览、查询、删除、修改和保存到文件的功能。学生信息用文件保存，可以不定时地增加学生信息。按学号查询和按姓名查询都是支持的。不允许修改学号的程序代码已经在修改学生信息的函数中实现。