No trees in the stdlib?

[João Valverde]

João Valverde wrote:
> Aahz wrote:
>> In article <mailman.2139.1245994218.8015.python-list at python.org>,
>> Tom Reed  <tomreed05 at gmail.com> wrote:
>>  
>>> Why no trees in the standard library, if not as a built in? I 
>>> searched the archive but couldn't find a relevant discussion. Seems 
>>> like a glaring omission considering the batteries included 
>>> philosophy, particularly balanced binary search trees. No interest, 
>>> no good implementations, something other reason? Seems like a good 
>>> fit for the collections module. Can anyone shed some light?
>>>     
>>
>> What do you want such a tree for?  Why are dicts and the bisect module
>> inadequate?  Note that there are plenty of different tree 
>> implementations
>> available from either PyPI or the Cookbook.
>>   
> A hash table is very different to a BST.  They are both useful. The 
> bisect module I'm not familiar with, I'll have to look into that, thanks.
>
> I have found pyavl on the web, it does the job ok, but there no 
> implementations for python3 that I know of.
>
> Simple example usage case: Insert string into data structure in sorted 
> order if it doesn't exist, else retrieve it.
>
After browsing the bisect module I don't think it is the complete 
answer. Please correct me if I'm mistaken but...

Ignoring for a moment that subjectively I feel this is not very pythonic 
for my use case, if I get back the insertion position, doesn't that mean 
I have to go over on average N/2 items on a linked list to insert the 
item in position? Maybe less for sophisticated implementations but still 
O(n)? That doesn't compare favorably to the cost of (possibly) having to 
rebalance a tree on insertion.