On Mon, 03 Mar 2014 18:02:04 -0500, Roy Smith wrote:
> In article <mailman.7669.1393885090.18130.python-l...@python.org>,
> Ben Finney <ben+pyt...@benfinney.id.au> wrote:
>
>> That's right. Python provides this singleton and then recommends you
>> compare with ‘is’, precisely to protect against pathological cases like
>> a “return True when compared for equality with None” data type.
>
> Going off on a tangent, I've often wished Python provided more kinds of
> None-ness. I'll often write:
>
> def f(arg=None):
> whatever
>
> where it would be nice to differentiate between "this was called with no
> arguments" and "this was called with an argument of None". Sure, I can
> work around that with things like **kwargs,
That's the hard way. The easy way is:
_SENTINEL = object()
def f(arg=_SENTINEL):
if arg is _SENTINEL:
...
If you really cared, you could implement your own None_ish_Type and
create as many named sentinels as you wish.
--
Steven
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