3.17---购物车练习

一、文件修改、登录注册、tail工具

# 1、编写文件修改功能，调用函数时，传入三个参数（修改的文件路径，要修改的内容，修改后的内容）既可完成文件的修改
def change(file_path,old_str,new_str):
    import os
    with open(rf"{file_path}",mode="rt",encoding="utf-8") as f,
        open(rf"new.txt",mode="wt",encoding="utf-8") as f1:
        while True:
            line = f.readline()
            res = line.replace(old_str,new_str)         # .replace()函数是返回一个新字符串，而非在原字符串上操作
            if not line:
                break
            f1.write(res)
    os.remove(rf"{file_path}")
    os.rename(rf"new.txt",rf"{file_path}")

# 2、编写tail工具
def tail(file_path):
    import time
    import os
    if os.path.exists(rf"{file_path}"):
        with open(rf"{file_path}",mode="rb") as f:
            f.seek(0,2)
            while True:
                line = f.readline()
                if line:
                    print(line.decode("utf-8"),end="")
                else:
                    time.sleep(0.5)
    else:
        with open(rf"{file_path}",mode="wb") as f:
            pass


# 3、编写登录功能
def login():
    import os
    if os.path.exists("logined.txt"):
        os.remove(r"logined.txt")                  # 文件必须存在 [WinError 2] 系统找不到指定的文件。: 'logined.txt'
    username = input("请输入账号：")
    password = input("请输入密码：")
    with open(r"user_data.txt",mode="rt",encoding="utf-8") as f:
        for line in f:
            name, pwd = line.strip().split(":")
            if name == username and password == pwd:
                print("登录成功！")
                with open(r"logined.txt",mode="wt",encoding="utf-8") as f1:
                    f1.write(rf"{username}")
                return username
        else:
            print("用户名或密码错误，登录失败！")

# 4、编写注册功能
def register():
    username = input("请输入注册账号：")
    with open(rf"user_data.txt",mode="r+t",encoding="utf-8") as f:
        for line in f:
            name, pwd = line.strip().split(":")
            if name == username:
                print("用户已存在！")
                break
        else:
            password = input("请设定密码：")
            f.write(f"{username}:{password}
")
            print(f"用户{username}注册成功！")

# 5、编写用户认证功能
def check():                        # 查看是否登录成功，若成功，返回登录账号，若失败返回None
    import os
    if os.path.exists(r"logined.txt"):
        with open(r"logined.txt",mode="rt",encoding="utf-8") as f:
            return f.read()
    else:
        print("请登录！")

二、购物车

# 选做题：编写ATM程序实现下述功能，数据来源于文件db.txt
# 1、充值功能：用户输入充值钱数，db.txt中该账号钱数完成修改
# 2、转账功能：用户A向用户B转账1000元，db.txt中完成用户A账号减钱，用户B账号加钱
# 3、提现功能：用户输入提现金额，db.txt中该账号钱数减少
# 4、查询余额功能：输入账号查询余额
def print_screen():
    print(" ATM服务 ".center(50,"-"),end="")
    print('''
1、充值功能
2、转账功能
3、提现功能
4、查询余额功能
5、登录
(r:回到登录界面，q:退出程序)''')
    print(" end ".center(50, "-"))

def search_name(file_path,name):
    with open(file_path,mode="rt",encoding="utf-8") as f:
        for line in f:
            if line:
                username, account = line.strip().split(":")
                if name == username:
                    return line
        else:
            return

def charge(login_name):
    num = input("请输入您的充值金额：")
    line = search_name(r"db.txt",login_name)
    if line:
        user_name , account = line.strip().split(":")
        account_num = float(account)
        account_num += float(num)
        account_num = str(account_num)
        new_line = f"{login_name}:{account_num}
"
        change("db.txt", line, new_line)
        print(f"充值成功{num}元！您的账户余额为：{account_num}元")
    else:
        with open(r"db.txt",mode = "at",encoding="utf-8") as f:
            f.write(f"{login_name}:{num}
")
            print(f"充值成功{num}元！您的账户余额为：{num}元")
    print("按Enter键继续。",end="")

def transfer(login_name):
    apt_user = input("请输入您需要转账的账户：")
    apt_line = search_name(r"db.txt",apt_user)
    if apt_line:
        num = input("请输入您需要转账的金额：")
        num = float(num)
        login_line = search_name(r"db.txt",login_name)
        if not login_line:
            with open(r"db.txt", mode="at", encoding="utf-8") as f:
                f.write(f"{login_name}:{0}
")
            login_line = f"{login_name}:{0}
"
        g_user, account = login_line.strip().split(":")
        account = float(account)
        if account >= num:
            a_user, apt_account = apt_line.strip().split(":")
            apt_account = float(apt_account)
            account -= num
            apt_account += num
            account = str(account)
            apt_account = str(apt_account)
            new_g = f"{g_user}:{account}
"
            new_apt = f"{a_user}:{apt_account}
"
            change(r"db.txt",login_line,new_g)
            change(r"db.txt",apt_line,new_apt)
            print(f"转账成功，您的账户余额为：{account}元。")
        else:
            print("余额不足，转账失败！")
    else:
        print("您需要转账的用户不存在！")
    print("按Enter键继续。",end="")

def Cash(login_name):
    num = input("请输入您需要提现的金额：")
    num = float(num)
    login_line = search_name(r"db.txt", login_name)
    g_user, account = login_line.strip().split(":")
    account = float(account)
    if account >= num:
        account -= num
        account = str(account)
        new_g = f"{g_user}:{account}
"
        change(r"db.txt", login_line, new_g)
        print(f"提现{num}元成功，您的账户余额为：{account}元。")
    else:
        print("余额不足，提现失败！")
    print("按Enter键继续。",end="")

def check_balance(name):
    line = search_name(r"db.txt",name)
    if line:
        user_name, account = line.strip().split(":")
        print(f"账户余额为：{account}元")
    else:
        with open(r"db.txt",mode = "at",encoding="utf-8") as f:
            f.write(f"{name}:{0}
")
        print("账户余额为：0")
    print("按Enter键继续。",end="")

import os
import time
tag = True
while tag:
    while tag:
        print(""*50)
        print_screen()
        command = input("请输入功能代码：")
        if os.path.exists("logined.txt"):
            if command == "1":
                charge(name)
                input("")
            elif command == "2":
                transfer(name)
                input("")
            elif command == "3":
                Cash(name)
                input("")
            elif command == "4":
                check_balance(name)
                input("")
            elif command == "5":
                name = login()
            elif command == "q" or command == "Q":
                tag = False
                os.remove("logined.txt")
            elif command == "r" or command == "R":
                os.remove("logined.txt")
                break
        else:
            print("请先登录！")
            time.sleep(1)