'is not' or '!='

[alister]

On Mon, 18 Aug 2014 23:53:49 +0300, Marko Rauhamaa wrote:

> "ElChino" <elchino at cnn.cn>:
> 
>> A newbie question to you; what is the difference between statements
>> like:
>>  if x is not None:
>> and if x != None:
> 
> Do the following: take two $10 bills. Hold one bill in the left hand,
> hold the other bill in the right hand.
> 
> Now, the bill in the left hand "is not" the bill in the right hand.
> However, the bill in the left hand "==" the bill in the right hand.
> 
>> Without any context, which one should be preferred?
>> IMHO, the latter is more readable.
> 
> In almost all cases, both tests would result in the same behavior.
> However, the "is not" test is conceptually the correct one since you
> want to know if x is the one and only None object. You don't want to be
> fooled by an imposter object that simply looks like the None object.
> Frankly, I don't know of any other object that is "==" to the None
> object except None itself, but such objects could possible exist.
> 
> 
> Marko

Depending on context you may 'Want' 0 to be equal to none
however as far as python is concerned it is not.




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