python – What is the difference between is None and == None

python – What is the difference between is None and == None

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.

class Foo:
    def __eq__(self,other):
        return True
foo=Foo()

print(foo==None)
# True

print(foo is None)
# False

python – What is the difference between is None and == None

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

Leave a Reply

Your email address will not be published. Required fields are marked *