how to convert code that uses cmp to python3

[Antoon Pardon]

Op 07-04-16 om 14:22 schreef Chris Angelico:

...

> There's no __cmp__ method, but you could easily craft your own
> compare() function:
> 
> def compare(x, y):
>     """Return a number < 0 if x < y, or > 0 if x > y"""
>     if x == y: return 0
>     return -1 if keyify(x) < keyify(y) else 1
> 
> I'm not sure how your tree is crafted and how your "cheap" and
> "expensive" comparisons previously worked, but give something like
> this a try. I think you'll find it adequate.

That solution will mean I will have to do about 100% more comparisons
than previously.

Lets simplify for the moment and suppose all keys are tuples of
integers. Now because how trees are organised, the lower you
descend in the tree, the closer the keys are together. In the
case of tuples that means higher probability you have to traverse
the two tuples further in order to find out which is greater.

With the __cmp__ method, you only had to traverse the two tuples
once in order to find out whether they were equal or if not which
is the smaller and which is the greater.

With this method I have to traverse the two tuples almost always
twice. Once to find out if they are equal and if not a second
time to find out which is greater.

-- 
Antoon.