Question about idioms for clearing a list

[Bryan Olson]

Magnus Lycka wrote:
> Bryan Olson wrote:
> 
>> Magnus Lycka wrote:
>>
>>> Do you really have a usecase for this? It seems to me that your
>>> argument is pretty hollow.
>>
>>
>> Sure:
>>
>>     if item_triggering_end in collection:
>>         handle_end(whatever)
>>         collection.clear()
>>
>> Or maybe moving everything from several collections into
>> a single union:
>>
>>     big_union = set()
>>     for collection in some_iter:
>>         big_union.update(t)
>>         collection.clear()
> 
> 
> I don't understand the second one. Where did 't' come from?

Cut-and-past carelessness. Meant to update with 'collection'.

> Anyway, tiny code snippets are hardly usecases.

The task is the usecase.

[...]
> I still don't see any convincing usecase for the kind of
> ducktyping you imply.

I didn't say I could convince you. I said that when different
types can support the same operation, they should also support
the same interface. That's what enables polymorphism.


-- 
--Bryan