Python 为什么使用“OR”检查多个值的变量只检查第一个值？
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Why does checking a variable against multiple values with `OR` only check the first value?
提问by Leon Gaban
I want to check if a variable has one of multiple values. I'm confused about why ordoesn't work in this situation. I was following a tutorial that gave the example if (a or b):, but when I try to do this it only checks the variable against the first value. What is wrong with my check?
我想检查一个变量是否具有多个值之一。我很困惑为什么or在这种情况下不起作用。我正在关注给出示例的教程if (a or b):，但是当我尝试执行此操作时，它仅根据第一个值检查变量。我的支票有什么问题？
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"
采纳答案by cdhowie
("Jesse" or "jesse")
The above expression tests whether or not "Jesse"evaluates to True. If it does, then the expression will return it; otherwise, it will return "jesse". The expression is equivalent to writing:
上面的表达式测试计算结果是否"Jesse"为True。如果是，则表达式将返回它；否则，它将返回"jesse"。该表达式等效于写作：
"Jesse" if "Jesse" else "jesse"
Because "Jesse"is a non-empty string though, it will alwaysevaluate to Trueand thus be returned:
因为它"Jesse"是一个非空字符串，所以它总是计算为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'
>>>
This means that the expression:
这意味着表达式：
name == ("Jesse" or "jesse")
is basically equivalent to writing this:
基本上相当于写这个：
name == "Jesse"
In order to fix your problem, you can use the inoperator:
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"):
Or, you can lowercase the value of namewith str.lowerand then compare it to "jesse"directly:
或者，您可以将namewith的值小写str.lower，然后"jesse"直接与它进行比较：
# This will also handle inputs such as "JeSSe", "jESSE", "JESSE", etc.
if name.lower() == "jesse":
回答by Sukrit Kalra
if name in ("Jesse", "jesse"):
would be the correct way to do it.
将是正确的方法。
Although, if you want to use or, the statement would be
虽然，如果你想使用or，语句将是
if name == 'Jesse' or name == 'jesse':
>>> ("Jesse" or "jesse")
'Jesse'
evaluates to 'Jesse', so you're essentially not testing for 'jesse'when you do if name == ("Jesse" or "jesse"), since it only tests for equality to 'Jesse'and does not test for 'jesse', as you observed.
评估为'Jesse'，因此您实际上并没有测试'jesse'何时执行if name == ("Jesse" or "jesse")，因为正如您所观察到的那样，它仅测试与 的相等性'Jesse'而不测试'jesse'。
回答by falsetru
If you want case-insensitive comparison, use loweror upper:
如果您想要不区分大小写的比较，请使用lower或upper：
if name.lower() == "jesse":
回答by cdhowie
The oroperator returns the first operand if it is true, otherwise the second operand. So in your case your test is equivalent to if name == "Jesse".
该or运算符返回第一个操作数，如果它是真实的，否则第二个操作数。因此，在您的情况下，您的测试等效于if name == "Jesse".
The correct application of orwould be:
的正确应用or是：
if (name == "Jesse") or (name == "jesse"):
