[Python-ideas] `numbers.Natural`

[Ram Rachum]

Hmm, I don't know, but I like it better. I probably had a reason and forgot
it. Sorry :(

On Fri, Sep 26, 2014 at 11:03 PM, David Mertz <mertz at gnosis.cx> wrote:

> Isn't the right answer to create an isNatural() function? Why do we need a
> type or class rather than just a function? It's not any easier to write
> 'isinstance(x, Natural)' than it is to write 'isNatural(x)'.
>
> On Fri, Sep 26, 2014 at 11:47 AM, Andrew Barnert <
> abarnert at yahoo.com.dmarc.invalid> wrote:
>
>> On Sep 26, 2014, at 11:37, Ram Rachum <ram at rachum.com> wrote:
>>
>> I checked it and you're right. So I guess `Hashable` is a bit confusing:
>>
>>     >>> isinstance(([3],), collections.Hashable)
>>     True
>>
>>
>> It makes sense if you think of isinstance as a type check, which is what
>> it's supposed to be, rather than a value check. ([3],) is a tuple, and
>> tuples are hashable as a type, even though some specific tuple values might
>> not be.
>>
>> That's exactly why I think you want a type that you can check for
>> Natural, rather than something about the value. That's what isinstance is
>> for, and if you start subverting it to mean other things, that's when it
>> leads to confusion.
>>
>>
>> On Fri, Sep 26, 2014 at 9:35 PM, Andrew Barnert <abarnert at yahoo.com>
>> wrote:
>>
>>> On Sep 26, 2014, at 11:13, Ram Rachum <ram at rachum.com> wrote:
>>>
>>> I agree with both the points you raised, they're both disadvantages. The
>>> question is whether the uses would be worth these two disadvantages.
>>> (`collections.Hashable` also has the second disadvantage you mentioned, and
>>> it's still in the stdlib, so there's hope.)
>>>
>>>
>>> Hashable doesn't have that disadvantage. It checks whether the object's
>>> class or any superclass has a __hash__ method. So it's still based on the
>>> type, not on the value, and it works as expected with issubclass.
>>>
>>>
>>> On Fri, Sep 26, 2014 at 9:10 PM, Thomas Gläßle <t_glaessle at gmx.de>
>>> wrote:
>>>
>>>>  At first glance it sounds nice and straight forward.
>>>> But - is a natural positive, or just non-negative? I guess, I'd have to
>>>> look it up in the docs each time, since either definition is used in lots
>>>> of places.
>>>> Also, Natural does not correspond to the python type, but its value.
>>>> So, you couldn't use it with issubclass.
>>>>
>>>>
>>>> Ram Rachum wrote on 09/26/2014 07:54 PM:
>>>>
>>>> I wish the `numbers` module would include a `Natural` class that would
>>>> simply check whether the number is integral and positive.
>>>>
>>>>
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