[Python-ideas] Fast sum() for non-numbers

[Serhiy Storchaka]

03.07.13 06:24, Mathias Panzenböck написав(ла):
> Such a function is very tiny:
>
>  >>> import operator
>  >>> isum = lambda *args: reduce(operator.iadd,*args)
>
> But this might be unexpected:
>
>  >>> l = []
>  >>> l2 = isum([[1,2,3]]*1000000, l)
>
> l is now changed. In fact l == l2. I guess this could cause more
> troubles than
> it's good for if the user expects tha current behaviour. I don't think
> such an
> incompatible API change can ever be made. But one could maybe include isum,
> maybe just as recipe in the documentation or in itertools or somewhere.

Sergey's code is more smart. It equals to the following Python code:

def sum(iterable, start=0):
     it = iter(iterable)
     try:
         x = next(it)
     except StopIteration:
         return start
     result = start + x
     for x in it:
         result += x
     return result