[Python-Dev] {}.popitem() (was Re: {}.first[key,value,item] ...)

[Moshe Zadka]

On Mon, 11 Dec 2000 15:22:55 -0500, "Tim Peters" <tim.one@home.com> wrote:

> Well, anyone can play.  When keys collide, what we need is a function f(i)
> such that repeating
>     i = f(i)
> visits every int in (0, 2**N) exactly once before setting i back to its
> initial value, for a fixed N and where the first i is in (0, 2**N).  

OK, maybe this is me being *real* stupid, but why? Why not [0, 2**n)?
Did 0 harm you in your childhood, and you're trying to get back? <0 wink>.

If we had an affine operation, instead of a linear one, we could have 
[0, 2**n). I won't repeat the proof here but changing

> def f(i):
>     i <<= 1
      i^=1 # This is the line I added
>     if i >= 2**N:
>        i ^= MAGIC_CONSTANT_DEPENDING_ON_N
>     return i

Makes you waltz all over [0, 2**n) if the original made you comple 
(0, 2**n). 

if-i'm-wrong-then-someone-should-shoot-me-to-save-me-the-embarrasment-ly y'rs,
Z.
-- 
Moshe Zadka <sig@zadka.site.co.il>
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