Python中or逻辑判断语句未按预期工作的问题求助

原代码 #

import time

repeat=0
price=0
print("Welcome to McDonald's self order system")
time.sleep(0.5)
name_person=str(input("\nPlease enter your name to continue: "))
while True:
    order=int(input("\n---Menu---\n 1.Burger\n 2.McPuff\n 3.Ice Cream\n 4.Cold Drink\n\nPlease order by typing the number: "))
    if order in range(1,4) :
        repeat=str(input("Do you want to order more? Yes/No: "))
        if repeat == "No" or "no":
            print("Ok")
            break
    else :
        print("\n!!Invalid input!!")
        time.sleep(0.5)

问题现象 #

输入“No”时程序正常退出，但输入“Yes”或其他任意内容时，也会触发“Ok”并退出循环；移除or "no"后功能恢复正常。

修复方案 #

问题出在or的逻辑写法上，以下两种写法都能解决问题：

写法1：完整的逻辑判断

import time

repeat=0
price=0
print("Welcome to McDonald's self order system")
time.sleep(0.5)
name_person=str(input("\nPlease enter your name to continue: "))
while True:
    order=int(input("\n---Menu---\n 1.Burger\n 2.McPuff\n 3.Ice Cream\n 4.Cold Drink\n\nPlease order by typing the number: "))
    if order in range(1,4) :
        repeat=str(input("Do you want to order more? Yes/No: "))
        # 修正or的逻辑：分别判断repeat等于"No"或"no"
        if repeat == "No" or repeat == "no":
            print("Ok")
            break
    else :
        print("\n!!Invalid input!!")
        time.sleep(0.5)

写法2：用in判断（更简洁）

import time

repeat=0
price=0
print("Welcome to McDonald's self order system")
time.sleep(0.5)
name_person=str(input("\nPlease enter your name to continue: "))
while True:
    order=int(input("\n---Menu---\n 1.Burger\n 2.McPuff\n 3.Ice Cream\n 4.Cold Drink\n\nPlease order by typing the number: "))
    if order in range(1,4) :
        repeat=str(input("Do you want to order more? Yes/No: "))
        # 检查输入是否在指定的集合中
        if repeat in {"No", "no"}:
            print("Ok")
            break
    else :
        print("\n!!Invalid input!!")
        time.sleep(0.5)

错误原因 #

原代码中的repeat == "No" or "no"在Python中会被解析为(repeat == "No") or "no"。由于非空字符串在布尔判断中会被视为True，所以不管repeat的值是什么，整个条件表达式的结果都是True，导致程序直接退出循环。

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