[Python-ideas] `numbers.Natural`

[David Mertz]

On Fri, Sep 26, 2014 at 1:57 PM, Thomas Gläßle <t_glaessle at gmx.de> wrote

> And more importantly: you wouldn't expect isNatural(3.5) to return True.
>

That's not a problem with my one-liner, nor Ian's:

>>> isNatural = lambda x: int(x)==x and x>0
>>> isNatural(3.5)
False

However, my correction to avoid crashing on some inputs is still wrong,
given:

>>> isinstance(0j, numbers.Number)
True
>>> int(0j)
TypeError

So I think I really need a couple lines:

    def isNatural(x):
        try:
            return int(x)==x and x>0
        except (TypeError, ValueError):
            return False

Of course... if you don't want that behavior, you need to write a different
function :-).


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