Python中if语句触发SyntaxError语法错误的求助

错误原因 #

你代码里的or if是明显的语法错误——Python的逻辑运算符or后面直接跟布尔判断表达式就行，不需要重复写if关键字，这就是触发SyntaxError的根本原因。

修复后的基础代码 #

把所有or if改成or，保留原有的判断逻辑，就能正常运行：

from time import sleep  # 补充导入sleep模块，避免运行报错

sleep(1)
print("Did lunch start before or after 12:00pm?")
while True:
    lunch_time = input()
    if lunch_time == "before" or lunch_time == "Before":
        avgrams *= 0.98
        STDEV *= 0.98
        break
    elif lunch_time == "after" or lunch_time == "After":
        break
    else:
        sleep(1)
        print("Sorry, I don't understand.")
        sleep(1)
        print("Please only answer with 'before' or 'after' (with no punctuation).")

更简洁的优化方案 #

可以把输入内容转成小写（同时去掉首尾空格），这样不用重复判断大小写，代码更简洁健壮，还能兼容用户输入的空格、大小写变体：

from time import sleep

sleep(1)
print("Did lunch start before or after 12:00pm?")
while True:
    # 转小写+去首尾空格，兼容用户输入的大小写、空格
    lunch_time = input().strip().lower()
    if lunch_time == "before":
        avgrams *= 0.98
        STDEV *= 0.98
        break
    elif lunch_time == "after":
        break
    else:
        sleep(1)
        print("Sorry, I don't understand.")
        sleep(1)
        print("Please only answer with 'before' or 'after' (with no punctuation).")

内容的提问来源于stack exchange，提问作者Morten