[Python-ideas] Why does `sum` use a default for the `start` parameter?

[Georg Brandl]

Vitor Bosshard schrieb:
> 2009/12/5 George Sakkis <george.sakkis at gmail.com>:
>> On Sat, Dec 5, 2009 at 6:45 PM, Andre Engels <andreengels at gmail.com> wrote:
>>
>>> On Sat, Dec 5, 2009 at 12:55 PM, Ram Rachum <cool-rr at cool-rr.com> wrote:
>>>> I noticed that `sum` tries to add zero to your iterable. Why? Why not just skip
>>>> adding any start value if none is specified?
>>>>
>>>> This current behavior is preventing me from using `sum` to add up a bunch of non-
>>>> number objects.
>>>
>>> In your proposed implementation, sum([]) would be undefined.
>>
>> Which would make it consistent with min/max.
> 
> 
> And in that case the special string handling could also be dropped?
> 
>>>> sum(["a","b"], "start")
> Traceback (most recent call last):
>   File "<pyshell#0>", line 1, in <module>
>     sum(["a","b"], "start")
> TypeError: sum() can't sum strings [use ''.join(seq) instead]
> 
> 
> This behaviour is quite bothersome. Sum can handle arbitrary objects
> in theory (as long as they define the correct special methods, etc.),
> but it gratuitously raises an exception on strings.

This seems to be an instance where the "practicality" Zen rule beats the
"special cases" rule :)

Georg

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