python - What is the difference between " is None " and " ==None "


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I recently came across this syntax, I am unaware of the difference.

I would appreciate it if someone could tell me the difference.


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    The answer is explained here.

    To quote:

    A class is free to implement comparison any way it chooses, and it can choose to make comparison against None mean something (which actually makes sense; if someone told you to implement the None object from scratch, how else would you get it to compare True against itself?).

    Practically-speaking, there is not much difference since custom comparison operators are rare. But you should use is None as a general rule.


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    class Foo:
        def __eq__(self,other):
            return True
    foo=Foo()
    
    print(foo==None)
    # True
    
    print(foo is None)
    # False
    

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    In this case, they are the same. None is a singleton object (there only ever exists one None).

    is checks to see if the object is the same object, while == just checks if they are equivalent.

    For example:

    p = [1]
    q = [1]
    p is q # False because they are not the same actual object
    p == q # True because they are equivalent
    

    But since there is only one None, they will always be the same, and is will return True.

    p = None
    q = None
    p is q # True because they are both pointing to the same "None"
    

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    If you use numpy,

    if np.zeros(3)==None: pass
    

    will give you error when numpy does elementwise comparison