Python字符串if判断失效 交易模拟程序逻辑bug排查

你的字符串判断失效完全是对Pythonor运算符的用法理解错误导致的：

• Python中所有非空字符串都属于布尔真值，a or b的运算逻辑是返回第一个为真的值，不是“匹配a或者匹配b”的意思
• 你写的proceed1 = "Checking" or "checking"执行后，proceed1只会被赋值为第一个真值也就是"Checking"，永远不会匹配小写的"checking"
• 同理deposit、withdraw、proceed2几个变量都只会存储首字母大写的那个字符串，只要用户输入小写内容就会匹配失败，出现分支跳转错乱的问题
• 额外逻辑bug：取款分支的余额计算写反了，你写的checking = withdraw1 - checking会得到负数余额，正确逻辑应该是原有余额减去取款金额；原代码只判断余额为0的情况，没有覆盖余额大于0但不足取款额的场景

不用提前定义那些带or的匹配变量，更稳妥的写法是把用户输入统一转为小写（或大写）后再做判断，不管用户输入大小写都能正常匹配，同时修正余额计算逻辑。修正后的完整代码如下：

import time
checking = 0
savings = 0

time.sleep(1)
print("Thank you for choosing the Bank of Kegan")
time.sleep(1)
choice = input("Type \"Deposit\" or \"Withdraw\" \n ").lower()
if choice == "deposit":
    print("Deposit Transaction Initiated")
    time.sleep(.5)
    print("Please choose an account you would like to Deposit into. ")
    account_choice = input("Type \"Checking\" or \"Savings\" \n ").lower()
    if account_choice == "checking":
        print("Checking Account Loading... \n")
        time.sleep(2)
        print("Checking: $", checking, "\n")
        time.sleep(2)
        amount1 = int(input("Please type how much you'd like to deposit. \n "))
        time.sleep(.5)
        print("$", amount1, "Transaction Pending...")
        time.sleep(2)
        checking += amount1
        print("Your new balance is: ")
        print("$", checking)

    elif account_choice == "savings":
        print("Savings Account Loading... ")
        time.sleep(2)
        print("Savings: $", savings)
        time.sleep(2)
        amount2 = int(input("Please type how much you'd like to deposit. \n "))
        time.sleep(.5)
        print("$", amount2, "Transaction Pending... ")
        time.sleep(2)
        savings += amount2
        print("Your new balance is: ")
        print("$", savings)
    else:
        print("Please choose a valid argument ")
elif choice == "withdraw":
    print("Withdraw Transaction Initiated")
    print("Type what account you would like to withdraw from. ")
    choice2 = input("Checking or Savings\n").lower()
    if choice2 == "checking":
        print("Checking Account Loading... ")
        time.sleep(2)
        print("Checking \n Balance: ", checking)
        withdraw1 = int(input("Type how much you would like to withdraw. "))
        print("$", withdraw1, "withdraw transaction pending... ")
        time.sleep(2)
        if checking < withdraw1:
            print("Insufficient balance, please check your account and try again.")
        else:
            checking -= withdraw1
            print("your new balance is: $", checking)
    elif choice2 == "savings":
        time.sleep(.5)
        print("Savings Account Loading... ")
        time.sleep(2)
        print("Savings \n Balance: ", savings)
        withdraw2 = int(input("Type how much you would like to withdraw. "))
        print("$", withdraw2, "withdraw transaction pending... ")
        time.sleep(2)
        if savings < withdraw2:
            print("Insufficient balance, please check your account and try again.")
        else:
            savings -= withdraw2
            print("your new balance is: $", savings)
    else:
        print("Please choose a valid argument.")

• 去掉了input()外面多余的str()转换，input()函数本身返回值就是字符串类型，不需要重复转换
• 把余额为0就提示没钱的判断改成了判断余额是否小于取款额，补上了余额大于0但不够取的逻辑漏洞
• 用+=、-=运算符简化余额计算的写法，更符合Python编码习惯
• 去掉了多余的exit()调用，分支执行完会自动结束对应逻辑，不需要手动退出

内容的提问来源于stack exchange，提问作者Kegan Bergeron