is != == (Re: [pygame] Sticky Variables: Terrain Loading)

[Toni Alatalo <antont@xxxxxxxxxxxxx>]

On Mar 12, 2008, at 5:43 AM, Ian Mallett wrote:

> Weird.  I get:
> >>> 2 is 1+1
> True

it's not too weird, it's just that 'is' is what you use to check if two 
references are to the same instance (object), and there's a pretty well 
known optimization in (c)Python that smallish numbers are kind of 
singletons so that they are not instanciated all the time

so use the == operator when interested in the values, and not whether 
the reference is the same.

'is' works well for "if x is None" because None is a singleton, i.e. 
all references to None point to the same object (that's why you better 
never do "None = 'x'" :p)

otherwise is useful for checking if a reference is exactly to the same 
object, e.g.:
a = SceneNode()
b = SceneNode(parent=a)
c = SceneNode(parent=a)
assert b.parent is c.parent

~Toni