is None or == None ?

[Alf P. Steinbach]

* mk:
> Hello,
> 
> Some claim that one should test for None using:
> 
> if x is None:
> 
> ..but the standard equality which is theoretically safer works as well:
> 
> if x == None:
> 
> So, which one is recommended?
> 
> Can there be two None objects in interpreter's memory? Is testing for 
> identity of some variable with None safe? Does language guarantee that? 
> Or is it just property of implementation?

As I understand it, 'is' will always work and will always be efficient (it just 
checks the variable's type), while '==' can depend on the implementation of 
equality checking for the other operand's class.


Cheers & hth.,

- Alf