sum() requires number, not simply __add__

Arnaud Delobelle arnodel at gmail.com
Thu Feb 23 22:41:28 CET 2012


On 23 February 2012 21:23, Buck Golemon <buck at yelp.com> wrote:
> def sum(values,
> base=0):
>      values =
> iter(values)
>
>      try:
>          result = values.next()
>      except StopIteration:
>          return base
>
>      for value in values:
>          result += value
>      return result

This is definitely not backward compatible.  To get something that has
a better chance of working with existing code, try this (untested):

_sentinel = object()

def sum(iterable, start=_sentinel):
    if start is _sentinel:
        iterable = iter(iterable)
        try:
            start = iterable.next()
        except StopIteration:
            return 0
    for x in iterable:
        start += x
    return start

del _sentinel

-- 
Arnaud



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