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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5 Answers

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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It depends on what you are comparing to None. Some classes have custom comparison methods that treat == None differently from is None.

In particular the output of a == None does not even have to be boolean !! - a frequent cause of bugs.

For a specific example take a numpy array where the == comparison is implemented elementwise:

import numpy as np a = np.zeros(3) # now a is array([0., 0., 0.]) a == None #compares elementwise, outputs array([False, False, False]), i.e. not boolean!!! a is None #compares object to object, outputs False
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If you use numpy,

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

will give you error when numpy does elementwise comparison