Python无类/模块实现银行系统：余额与现金无法更新问题

问题概述 #

作为Python新手，尝试不使用类或特定模块实现银行系统，已完成登录、注册、查询余额/持有现金功能，但执行存款（deposit）或取款（withdraw）操作后，账户余额（balance）与持有现金（cash）无法更新到文件中。

账户数据格式（每行4个字段，空格分隔）：

用户名 密码 余额 持有现金
示例：

aaa aaa 1 1
bkhg lkhg 1 1
terat rtrt 1 1
aa aa 1 1

核心问题分析 #

• 存款函数无文件更新逻辑：deposit仅修改了全局变量，完全没有将新余额写入文件的代码。
• 取款函数文件更新逻辑混乱：计算完新的持有现金后，又将变量覆盖为文件旧值，且用追加模式写入，未替换原数据。
• 文件操作模式错误：更新账户数据需要读取全部内容，修改对应行后重新写入，而非追加。
• 注册字段缺失：注册时只写入3个字段，缺少持有现金字段，导致后续查询出错。
• 变量类型转换混乱：反复在字符串和整数间转换，易引发逻辑错误。

修复后的完整代码 #

# 全局变量，存储当前登录用户的余额和持有现金
current_balance = 0
current_cash = 0
USER_FILE = "accounts.txt"

print("Welcome To the Bank")

def withdraw():
    global current_cash, current_balance
    while True:
        amounts_input = input("How much do you want to withdraw? $\n(exit) or (back) or (amount)\n")
        
        if amounts_input == "exit":
            quit()
        elif amounts_input == "back":
            break
        elif amounts_input.isdigit():
            amounts = int(amounts_input)
            if 0 < amounts <= current_cash:
                # 更新内存数值：现金减少，余额增加
                current_cash -= amounts
                current_balance += amounts
                # 更新文件数据
                update_account_data()
                print(f"{amounts}$ Has been withdrawn into your account!")
                back_or_exit = input("If you want to go back (back) or If you want to exit (exit)\n")
                if back_or_exit == "back":
                    break
                elif back_or_exit == "exit":
                    quit()
            elif amounts <= 0:
                print("We cannot accept 0 or less than that!")
            else:
                print("You don't have enough cash with you!")
        else:
            print("Enter a valid number to withdraw!")

def deposit():
    global current_balance, current_cash
    while True:
        amount_input = input("How much amount you want to deposit? $\n(exit) or (back) or (amount)\n")
        
        if amount_input == "exit":
            quit()
        elif amount_input == "back":
            break
        elif amount_input.isdigit():
            amount = int(amount_input)
            if 0 < amount <= current_balance:
                # 更新内存数值：余额减少，现金增加
                current_balance -= amount
                current_cash += amount
                # 更新文件数据
                update_account_data()
                print(f"{amount}$ Has been deposited from your account!")
                back_or_exit = input("If you want to go back (back) or If you want to exit (exit)\n")
                if back_or_exit == "back":
                    break
                elif back_or_exit == "exit":
                    quit()
            elif amount <= 0:
                print("We cannot accept 0 or less than that!")
            else:
                print("You don't have enough currency in your account!")
        else:
            print("Enter a valid number to deposit!")

def update_account_data():
    """将当前登录用户的最新余额和现金写入文件"""
    global username, password, current_balance, current_cash
    # 读取所有账户数据
    with open(USER_FILE, "r") as f:
        lines = f.readlines()
    # 修改对应账户的行
    updated_lines = []
    for line in lines:
        line = line.strip()
        if not line:
            continue
        parts = line.split()
        if parts[0] == username and parts[1] == password:
            updated_line = f"{username} {password} {current_balance} {current_cash}\n"
            updated_lines.append(updated_line)
        else:
            updated_lines.append(line + "\n")
    # 重新写入文件
    with open(USER_FILE, "w") as f:
        f.writelines(updated_lines)

def find_balance_and_cash():
    """查询当前登录用户的余额和现金，存入全局变量"""
    global username, password, current_balance, current_cash
    with open(USER_FILE, "r") as f:
        for line in f.readlines():
            line = line.strip()
            if not line:
                continue
            parts = line.split()
            if parts[0] == username and parts[1] == password:
                current_balance = int(parts[2])
                current_cash = int(parts[3])
                return

def login():
    """验证登录信息，成功返回True，失败退出"""
    global username, password
    with open(USER_FILE, "r") as f:
        for line in f.readlines():
            line = line.strip()
            if not line:
                continue
            parts = line.split()
            if parts[0] == username and parts[1] == password:
                print("Correct credentials!")
                return True
    print("Incorrect credentials.")
    quit()

def register():
    """注册新账户，默认余额和现金为1"""
    usernamee = input("Please input your desired name\n")
    passwordd = input("Please input your desired password\n")
    # 写入完整4个字段
    with open(USER_FILE, "a") as f:
        f.write(f"{usernamee} {passwordd} 1 1\n")
    print("Registration successful!")

# 登录/注册流程
while True:
    log_choice = input("(Login) or (Register) or (Exit)\n").lower()
    if log_choice == "login":
        username = input("Please enter your username\n")
        password = input("Please enter your password\n")
        login()
        find_balance_and_cash()
        break
    elif log_choice == "register":
        register()
        break
    elif log_choice == "exit":
        quit()
    else:
        print("Sorry It Seems Like You Have Typed The Wrong Answer :( Try Again!")

print(f"You have {current_balance}$ in your account and {current_cash}$ cash with you!")

# 主操作循环
while True:
    choice = input("Here is a choice for you\n(exit) (withdraw) (deposit)\n").lower()
    if choice == "deposit":
        deposit()
        print(f"Current status: {current_balance}$ in account, {current_cash}$ cash")
    elif choice == "withdraw":
        withdraw()
        print(f"Current status: {current_balance}$ in account, {current_cash}$ cash")
    elif choice == "exit":
        quit()
    else:
        print("Sorry it seems like you have typed wrong answer")

关键修改说明 #

• 新增update_account_data函数：专门处理文件更新，通过读取所有行、修改目标行、重新写入的方式替换原数据，避免追加模式的问题。
• 修复存取款逻辑：明确存取款时的数值变化关系，操作后立即调用文件更新函数，移除混乱的变量覆盖逻辑，直接操作全局整数变量。
• 修复注册函数：写入完整4个字段，符合数据格式要求。
• 合并查询函数：将两个查询函数合并为一个，一次获取余额和现金，简化逻辑。
• 优化文件操作：使用with语句自动管理文件生命周期，避免资源泄漏。

内容的提问来源于stack exchange，提问作者sainbileg