为什么用`或`检查一个变量的多个值时只检查第一个值？[副本]

Question

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“Jesse”的计算结果是否为true。如果是，那么表达式将返回它；否则，它将返回“Jesse”。表达式相当于写：

"Jesse" if "Jesse" else "jesse"

因为“Jesse”是非空字符串，所以它的计算结果总是true，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")

name == "Jesse"

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

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