I recently came across this syntax, I am unaware of the difference.
I would appreciate it if someone could tell me the difference.
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.
17 Comments
Nas Banov
Also,
is None is a bit (~50%) faster than == None :)Nas Banov
@myusuf3: >>> timeit.Timer('None is None').timeit() | 0.225 | >>> timeit.Timer('None == None').timeit() | 0.328
Pijusn
@myusuf3 You don't really need a proof for that.
is is, basically, integer comparison while == is not only resolving references but comparing values which may have mismatching types.
Jblasco
One on favour of "is". When a variable can be either None or something that has no meaningful comparison with None. For example, a variable can be a numpy.array or None (my particular case).
Yuval
I would like to add to what @TimLudwinski is saying: first, if someone chose to override the equality operator to make None a special case, why would we want to tell them otherwise? Second, "There should be one-- and preferably only one --obvious way to do it." And the obvious way to check if something is equal to something is, well, the equality operator.
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class Foo: def __eq__(self, other): return True foo = Foo() print(foo == None) # True print(foo is None) # False 
2 Comments
fuenfundachtzig
See stackoverflow.com/a/26611/143931 for some interesting comments on this answer.
Don Feto
This is very good example to show that is None can't be missed, while ==None can be missed with.
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" 
2 Comments
max
This answer is not correct, as explained in Ben Hoffstein's answer below stackoverflow.com/questions/3257919/is-none-vs-none/….
x == None may evaluate to True even if x is not None but an instance of some class with its own custom equality operator.
colidyre
Additionally, it would be also good to have a definition or further explanations what equivalent exactly means.
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 
2 Comments
Olsgaard
I think this is a better answer than the current accepted answer, as it has easy to understand examples.
Kay
This answer can be improved since, a is not None, it is an array and its constituents are also not None. A better example would be:
arr = np.array([1, 2, 3, 4, None]) arr == None
==andisin python?isvs==, or about the nature of what exactlyNoneis and how the behaviour differs in either context (the latter is why I ended up here). Based on the vagueness and lack of OP responses... I'm surprised this has so many upvotes. I mean... cmon... the question is not even written in the actual question...