用Python编写程序，模拟实现一个四则运算练习模拟系统。用户分为老师用户和学生用户。老师用户登录后，可以管理题目信息和学生信息，并统计成绩；学生登录后，可随机在题库抽取N个题目完成题目练习，并可查看本次成绩或之前的所有成绩。要求所有信息都保存在d:\\temp\\unit9文件中。

以下实现该功能的Python代码：

import os
import random

# 检查文件夹和文件是否存在，不存在则创建
if not os.path.exists("d:\\temp\\unit9"):
    os.mkdir("d:\\temp\\unit9")
filename = "d:\\temp\\unit9\\exercise.txt"
if not os.path.exists(filename):
    file = open(filename, "w")
    file.write("1+1=2\n")
    file.write("2+2=4\n")
    file.write("3+3=6\n")
    file.write("4+4=8\n")
    file.write("5+5=10\n")
    file.close()

filename = "d:\\temp\\unit9\\score.txt"
if not os.path.exists(filename):
    file = open(filename, "w")
    file.close()

# 登录界面
while True:
    print("=" * 30)
    print("欢迎使用四则运算练习模拟系统")
    print("1.老师用户登录")
    print("2.学生用户登录")
    print("3.退出系统")
    choice = input("请选择：")
    if choice == "1":
        # 老师用户登录
        print("=" * 30)
        print("欢迎老师用户登录")
        username = input("请输入用户名：")
        password = input("请输入密码：")
        if username == "admin" and password == "123456":
            while True:
                print("=" * 30)
                print("请选择操作：")
                print("1.添加题目")
                print("2.删除题目")
                print("3.修改题目")
                print("4.查看题目")
                print("5.添加学生")
                print("6.删除学生")
                print("7.修改学生")
                print("8.查看学生")
                print("9.统计成绩")
                print("10.返回上一级菜单")
                choice = input("请选择：")
                if choice == "1":
                    # 添加题目
                    question = input("请输入题目内容：")
                    file = open("d:\\temp\\unit9\\exercise.txt", "a")
                    file.write(question + "\n")
                    file.close()
                    print("题目已添加。")
                elif choice == "2":
                    # 删除题目
                    file = open("d:\\temp\\unit9\\exercise.txt", "r")
                    lines = file.readlines()
                    file.close()
                    file = open("d:\\temp\\unit9\\exercise.txt", "w")
                    question = input("请输入要删除的题目：")
                    deleted = False
                    for line in lines:
                        if line.strip() == question:
                            deleted = True
                            print("题目已删除。")
                        else:
                            file.write(line)
                    file.close()
                    if not deleted:
                        print("未找到要删除的题目。")
                elif choice == "3":
                    # 修改题目
                    file = open("d:\\temp\\unit9\\exercise.txt", "r")
                    lines = file.readlines()
                    file.close()
                    file = open("d:\\temp\\unit9\\exercise.txt", "w")
                    question = input("请输入要修改的题目：")
                    modified = False
                    for line in lines:
                        if line.strip() == question:
                            modified = True
                            new_question = input("请输入新的题目内容：")
                            file.write(new_question + "\n")
                            print("题目已修改。")
                        else:
                            file.write(line)
                    file.close()
                    if not modified:
                        print("未找到要修改的题目。")
                elif choice == "4":
                    # 查看题目
                    file = open("d:\\temp\\unit9\\exercise.txt", "r")
                    lines = file.readlines()
                    file.close()
                    for line in lines:
                        print(line.strip())
                elif choice == "5":
                    # 添加学生
                    student = input("请输入学生姓名：")
                    file = open("d:\\temp\\unit9\\score.txt", "a")
                    file.write(student + ":0\n")
                    file.close()
                    print("学生已添加。")
                elif choice == "6":
                    # 删除学生
                    file = open("d:\\temp\\unit9\\score.txt", "r")
                    lines = file.readlines()
                    file.close()
                    file = open("d:\\temp\\unit9\\score.txt", "w")
                    student = input("请输入要删除的学生姓名：")
                    deleted = False
                    for line in lines:
                        if line.startswith(student + ":"):
                            deleted = True
                            print("学生已删除。")
                        else:
                            file.write(line)
                    file.close()
                    if not deleted:
                        print("未找到要删除的学生。")
                elif choice == "7":
                    # 修改学生
                    file = open("d:\\temp\\unit9\\score.txt", "r")
                    lines = file.readlines()
                    file.close()
                    file = open("d:\\temp\\unit9\\score.txt", "w")
                    student = input("请输入要修改的学生姓名：")
                    modified = False
                    for line in lines:
                        if line.startswith(student + ":"):
                            modified = True
                            new_score = input("请输入新的成绩：")
                            file.write(student + ":" + new_score + "\n")
                            print("学生已修改。")
                        else:
                            file.write(line)
                    file.close()
                    if not modified:
                        print("未找到要修改的学生。")
                elif choice == "8":
                    # 查看学生
                    file = open("d:\\temp\\unit9\\score.txt", "r")
                    lines = file.readlines()
                    file.close()
                    for line in lines:
                        print(line.strip())
                elif choice == "9":
                    # 统计成绩
                    file = open("d:\\temp\\unit9\\score.txt", "r")
                    lines = file.readlines()
                    file.close()
                    total_score = 0
                    for line in lines:
                        score = int(line.strip().split(":")[1])
                        total_score += score
                    print("总成绩为：", total_score)
                elif choice == "10":
                    # 返回上一级菜单
                    break
                else:
                    print("输入有误，请重新输入。")
        else:
            print("用户名或密码错误，请重新登录。")
    elif choice == "2":
        # 学生用户登录
        print("=" * 30)
        print("欢迎学生用户登录")
        username = input("请输入用户名：")
        password = input("请输入密码：")
        if os.path.exists("d:\\temp\\unit9\\score.txt"):
            file = open("d:\\temp\\unit9\\score.txt", "r")
            lines = file.readlines()
            file.close()
            for line in lines:
                if line.startswith(username + ":"):
                    pwd = line.strip().split(":")[1]
                    if password == pwd:
                        print("登录成功。")
                        while True:
                            print("=" * 30)
                            print("请选择操作：")
                            print("1.开始练习")
                            print("2.查看本次成绩")
                            print("3.查看所有成绩")
                            print("4.返回上一级菜单")
                            choice = input("请选择：")
                            if choice == "1":
                                # 开始练习
                                file = open("d:\\temp\\unit9\\exercise.txt", "r")
                                lines = file.readlines()
                                file.close()
                                num = int(input("请输入要抽取的题目数量："))
                                random_lines = random.sample(lines, num)
                                score = 0
                                for line in random_lines:
                                    print(line.strip())
                                    answer = input("请输入答案：")
                                    if answer == line.strip().split("=")[1]:
                                        score += 10
                                print("本次得分为：", score)
                                file = open("d:\\temp\\unit9\\score.txt", "r")
                                lines = file.readlines()
                                file.close()
                                file = open("d:\\temp\\unit9\\score.txt", "w")
                                for line in lines:
                                    if line.startswith(username + ":"):
                                        file.write(username + ":" + str(score) + "\n")
                                    else:
                                        file.write(line)
                                file.close()
                            elif choice == "2":
                                # 查看本次成绩
                                file = open("d:\\temp\\unit9\\score.txt", "r")
                                lines = file.readlines()
                                file.close()
                                for line in lines:
                                    if line.startswith(username + ":"):
                                        print("本次成绩为：", line.strip().split(":")[1])
                            elif choice == "3":
                                # 查看所有成绩
                                file = open("d:\\temp\\unit9\\score.txt", "r")
                                lines = file.readlines()
                                file.close()
                                for line in lines:
                                    if line.startswith(username + ":"):
                                        print(line.strip())
                            elif choice == "4":
                                # 返回上一级菜单
                                break
                            else:
                                print("输入有误，请重新输入。")
                        break
            else:
                print("用户名或密码错误，请重新登录。")
        else:
            print("未找到学生信息，请联系老师添加。")
    elif choice == "3":
        # 退出系统
        break
    else:
        print("输入有误，请重新输入。")

该程序实现了一个简单的四则运算练习模拟系统，包括老师用户和学生用户两种角色。老师用户可以管理题目信息和学生信息，并统计成绩；学生用户可以随机抽取题目进行练习，并查看成绩。所有信息都保存在d:\\temp\\unit9文件夹中，其中题目信息保存在exercise.txt文件中，学生信息保存在score.txt文件中。