How to test if an object IS another object?
bdesth.quelquechose at free.quelquepart.fr
Sun Jun 12 22:52:51 CEST 2005
eloff777 at yahoo.com a écrit :
> Sorry about removing my message, I posted with the wrong google
> account, I don't really want my email where those irritating spam bots
> can find it.
>>The most obvious way (as usual ?):
>>if obj1 is obj2:
>> // your code here
> I immediately thought of is, and tested it in the console, but it
> didn't work quite like I expected:
>>foo = 3
>>bar = 3
>>zoo = foo
>>foo is zoo
>>foo is bar
>>zoo is bar
> clearly foo and bar have the same value but they are different objects
> aren't they?
Nope. They are two different names bound to the same integer object. You
may have similar situation with strings:
>>> s1 = "toto"
>>> s2 = "toto"
>>> s1 is s2
This is an application of the lightweight pattern. The Python
interpreter reuse the same "value object" to avoid memory clutter. Since
ints and strings are immutable, this is perfectly safe (but yet
confusing when you're not aware of this).
> Yet applying the is operator yields True.
Yes. But now you know why !-)
And don't worry, this is quite unlikely that it will cause you any
trouble in real code.
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