What is the difference between "foo is None" and "foo == None"

The difference between "foo is None" and "foo == None" is: the difference in judgers. The is judger is used to compare whether two objects are the same object, and the == judger is used to compare two objects. Whether the values ​​of the objects are equal.

The difference between foo is None and foo == None

if foo is None: 
    pass
if foo == None: 
    pass

These are two different usages, they What's the difference?

SolutionAnswer:

The variables themselves in Python do not store their values. Variable assignment actually points the variable reference to an object cached in memory. itself, for example:

a=5
b=5

It seems that the two variables actually point to the same object. At this time, a==b, a is b are both True, and the == operator compares the values ​​​​of the two objects. is determines whether two variables point to the same reference. If you want to determine whether it is the same object, use the function id() to display the identification of the actual object (an integer). At this time, id(a), id(b), id( 5) The identifiers are all consistent.

Similarly, if foo is None, it actually points to the actual identifier of the None object. At this time, use id() to display the identifier of any variable that is None, and you will find that it is the same as id(None) The results are the same.

The results in the question are the same, but the semantics are different. It depends on whether you want to express "foo and None are the same object" or "the value of foo is equal to the value of None".

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