sum() requires number, not simply __add__

Arnaud Delobelle arnodel at
Thu Feb 23 23:09:13 CET 2012

On 23 February 2012 22:04, Chris Angelico <rosuav at> wrote:
> On Fri, Feb 24, 2012 at 8:59 AM, Arnaud Delobelle <arnodel at> wrote:
>> def sum(iterable, start=_sentinel, _sentinel=_sentinel):
> Is this a reason for Python to introduce a new syntax, such as:
> def foo(blah, optional=del):
>    if optional is del: print("No argument was provided")
> Basically, 'del' is treated like a unique non-providable object, only
> possible in an argument list and only if the argument was omitted. No
> more proliferation of individual sentinels... what do you think?

The problem with these proposals is to avoid the leakage of 'del'.
Here you could do:

def get_del(x=del):
    return x

And then you're in trouble again.


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