list.pop(0) vs. collections.dequeue

Alf P. Steinbach alfps at start.no
Tue Jan 26 02:13:18 CET 2010


* Ethan Furman:
> Steve Howell wrote:
>>> On Sat, 23 Jan 2010 09:57:04 -0500, Roy Smith wrote:
>>>> So, we're right back to my statement earlier in this thread that the
>>>> docs are deficient in that they describe behavior with no hint about
>>>> cost. Given that, it should be no surprise that users make incorrect
>>>> assumptions about cost.
> 
> No hint?  Looking at the below snippet of docs -- "not efficient" and 
> "slow" sound like pretty good hints to me.
> 
>> Bringing this thread full circle, does it make sense to strike this
>> passage from the tutorial?:
>>
>> '''
>> It is also possible to use a list as a queue, where the first element
>> added is the first element retrieved (“first-in, first-out”); however,
>> lists are not efficient for this purpose. While appends and pops from
>> the end of list are fast, doing inserts or pops from the beginning of
>> a list is slow (because all of the other elements have to be shifted
>> by one).
>> '''
>>
>> I think points #3 and #6 possibly apply. Regarding points #2 and #4,
>> the tutorial is at least not overly technical or specific; it just
>> explains the requirement to shift other elements one by one in simple
>> layman's terms.
>>
> 
> I think the paragraph is fine.  Instead of waiting for the (hundreds 
> of?) posts wondering why making a FIFO queue from a list is so slow, and 
> what's wrong with Python, etc, etc, it points out up front that yes you 
> can, and here's why you don't want to.  This does not strike me as too 
> much knowledge.

Is the tutorial regarded as part of the language specification?

I understand that the standard library docs are part (e.g. 'object' is only 
described there), and that at least some PEPs are.


Cheers,

- Alf



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