Top and Bottom Values [PEP: 326]

[Georg Brandl]

Antoon Pardon wrote:
> On 2006-09-27, George Sakkis <george.sakkis at gmail.com> wrote:
>> Antoon Pardon wrote:
>>
>>> What bothers me a bit about the rejection of PEP 326 is that one of the
>>> reasons stated is:
>>>
>>>   http://mail.python.org/pipermail/python-dev/2004-January/042306.html
>>>
>>>   - it is easily implemented when you really need it
>>>
>>> Well I thought it would simplify some things for me, so I tried an
>>> implementation and then found that some of the things that I would
>>> want to do with it wont work. So the "is easily implemented" bit
>>> seems not to be correct.
>>
>> IIRC, the PEP proposed the Smallest and Largest singletons with the
>> sole purpose of being used in comparisons. No numeric behavior was
>> implied, i.e. Smallest and Largest are not negative and positive
>> infinity in the math sense of the word.
> 
> That is true.
> 
>> So I guess the "easily implemented" refers to this case alone.
> 
> This doesn't follow. Take the example were I got stuck.
> 
>>>> lst = range(10)
>>>> lst[:Top]

FWIW, this works with 2.5 and the __index__ slot:

 >>> class Top(object):
...  def __index__(self):
...   return sys.maxint
...
 >>> a=range(5)
 >>> a[:Top()]
[0, 1, 2, 3, 4]
 >>>

Georg