how to convert code that uses cmp to python3

[Marko Rauhamaa]

Ian Kelly <ian.g.kelly at gmail.com>:

> On Fri, Apr 8, 2016 at 10:33 AM, Marko Rauhamaa <marko at pacujo.net> wrote:
>> Ian Kelly <ian.g.kelly at gmail.com>:
>>
>>> That's fine for those operations and probably insert, but how do you
>>> search an AVL tree for a specific key without also using __eq__?
>>
>> Not needed:
>>
>> ========================================================================
>> if key < node.key:
>>     look_right()
>> elif node.key < key:
>>     look_left()
>> else:
>>     found_it()
>> ========================================================================
>
> That makes me a little nervous since it assumes that the keys are
> totally ordered and could return an incorrect node if they aren't.

That's all the more reason to tie the order explicitly to < and nothing
else.

> Granted, the keys *should* be totally ordered if the data structure is
> being used properly, but an explicit equality check ensures that the
> worst that could happen is the node simply isn't found despite being
> present.

Well, how do you know how __eq__ and __lt__ are related?

Better simply *define* a *match* as

   not key < node.key and not node.key < key

> More to the contextual point, this is still doing two comparisons,
> even if both of them are less than, so it doesn't really solve the
> OP's issue.

I'm not sure the OP has a real issue. If *that* is a real issue, I
recommend a different programming language. Thing is, I bet method calls
are the single most expensive Python operation, yet would anyone suggest
avoiding method calls?


Marko