[Python-ideas] `numbers.Natural`

[David Mertz]

Well, yeah. I think I lost that discussion in the type annotation thread
though. I'd love types to include predicates, but Guido wouldn't 😏.  An
'is_natural()' function--by whichever spelling--needs to contain a test
which isn't in the type system, whichever result one chooses for
'is_natural(1.0)'.

FWIW, I want 'isNatural(0j+1) == True'. But I'm on the losing end of at
least three arguments there.... Unless I just roll my own in 5-8 lines of
code.[*]

[*] I'd want the non-PEP8 spelling because "Natural" in mathematics is
always capitalized.  That's why we have the built-in 'isGuido(BDFL)' rather
than 'is_guido()'.
On Sep 26, 2014 4:42 PM, "Ben Finney" <ben+python at benfinney.id.au> wrote:

> David Mertz <mertz at gnosis.cx> writes:
>
> > Isn't the right answer to create an isNatural() function?
>
> No, the right answer (by PEP 8) is to create an ‘is_natural’ or
> ‘isnatural’ function :-)
>
> > Why do we need a type or class rather than just a function?
>
> Less facetiously: I suspect what is being asked for here is a type which
> will *ensure* the values are natural numbers.
>
> That is a good use of types, IMO: they enforce a domain of values.
>
> I'm not convinced there is a pressing need to add such a type to the
> standard type hierarchy though.
>
> --
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> Ben Finney
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