为什么用`OR`对照多个值检查变量仅检查第一个值？

Question

我想检查一个变量是否具有多个值之一。我对为什么or在这种情况下不起作用感到困惑。我正在按照给出该示例的教程进行操作if (a or b):，但是当我尝试执行此操作时，它只会根据第一个值检查变量。我的支票怎么了？

name = raw_input('Please type in your name:')

if len(name) < 5:
    print "Your name has fewer than 5 characters"
elif len(name) == 5:
    print "Your name has exactly 5 characters"
    if name == ("Jesse" or "jesse"):
        print "Hey Jesse!"
else:
    print "Your name has greater than 5 characters"

Answer 1

(“Jesse” or “jesse”)

上面的表达式测试是否"Jesse"评估为True。如果是这样，则表达式将返回它；否则，它将返回"jesse"。该表达式等同于编写：

"Jesse" if "Jesse" else "jesse"

因为"Jesse"是一个非空字符串，所以它将 始终 求值为True并因此返回：

>>> bool("Jesse")  # Non-empty strings evaluate to True in Python
True
>>> bool("")  # Empty strings evaluate to False
False
>>>
>>> ("Jesse" or "jesse")
'Jesse'
>>> ("" or "jesse")
'jesse'
>>>

这意味着表达式：

name == ("Jesse" or "jesse")

基本上等同于编写此代码：

name == "Jesse"

为了解决您的问题，您可以使用in运算符：

# Test whether the value of name can be found in the tuple ("Jesse", "jesse")
if name in ("Jesse", "jesse"):

或者，您可以小写namewith的值，str.lower然后将其"jesse"直接与进行比较：

# This will also handle inputs such as "JeSSe", "jESSE", "JESSE", etc.
if name.lower() == "jesse":