Is empty string cached?

[Farshid Lashkari]

> It takes far too little evidence to induce belief:
> 
>  >>> a = "hello"
>  >>> b = "h"+"ello"
>  >>> a is b
> False
>  >>> c = "hello"
>  >>> b is a
> False
>  >>>

I don't understand the point of your last expression. Were you intending 
this instead:

 >>> c is a
True

However, the following commands add to my confusion:

 >> a = 'wtf?'
 >> b = 'wtf?'
 >> a is b
False

So how are string literals cached? Is there an explanation somewhere? Is 
it some freaky voodoo, and I should just assume that a string literal 
will always generate a new object?

Thanks,
Farshid