[Tutor] Why begin a function name with an underscore

[Peter Otten]

eryksun wrote:

> On Tue, Aug 28, 2012 at 6:00 AM, Peter Otten <__peter__ at web.de> wrote:
>>
>> Anyway here's an alternative implementation:
>>
>>>>> def vi(x):
>> ...     if not isinstance(x, numbers.Number):
>> ...             raise TypeError
>> ...     if not int(x) == x:
>> ...             raise ValueError
> 
> You could test against numbers.Integral. 

That would reject "floats with an integral value" and therefore doesn't 
comply with the -- non-existing -- spec.

> But it's not fool-proof.

Nothing is. The code attempts to make expectations more explicit than Steven 
did in his original implementation.

> Someone can register an incompatible class with the abstract base
> class (ABC).
> 
>     >>> import numbers
>     >>> isinstance("42", numbers.Integral)
>     False
>     >>> numbers.Integral.register(str)
>     >>> isinstance("42", numbers.Integral)
>     True

That's quite an elaborate scheme to shoot yourself in the foot ;)