sum() requires number, not simply __add__

[Chris Angelico]

On Fri, Feb 24, 2012 at 8:59 AM, Arnaud Delobelle <arnodel at gmail.com> 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?

(I picked "del" because it's an existing keyword. Fairly arbitrary
choice though.)

Chris Angelico