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Date: Tue, 4 Mar 2014 10:09:28 +1100
Subject: Re: Reference
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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Xref: csiph.com comp.lang.python:67616

On Tue, Mar 4, 2014 at 10:02 AM, Roy Smith <roy@panix.com> wrote:
> In article <mailman.7669.1393885090.18130.python-list@python.org>,
>  Ben Finney <ben+python@benfinney.id.au> wrote:
>
>> That's right. Python provides this singleton and then recommends you
>> compare with =E2=80=98is=E2=80=99, precisely to protect against patholog=
ical cases like
>> a =E2=80=9Creturn True when compared for equality with None=E2=80=9D dat=
a type.
>
> Going off on a tangent, I've often wished Python provided more kinds of
> None-ness.  I'll often write:
>
> def f(arg=3DNone):
>    whatever
>
> where it would be nice to differentiate between "this was called with no
> arguments" and "this was called with an argument of None".

That's why you have your own sentinel.

_NONE_PASSED=3Dobject()
def f(arg=3D_NONE_PASSED):
    if f is not _NONE_PASSED: pass

ChrisA