[Python-ideas] Dunder method to make object str-like

[Terry Reedy]

On 4/7/2016 11:03 AM, Ethan Furman wrote:
> On 04/07/2016 07:07 AM, Random832 wrote:
>
>> What's __index__ for?
>
> __index__ is a way to get an int from an int-like object without losing
> information; so it fails with values like 3.4, but should succeed with
> values like Fraction(4, 2).
>
> __int__ is a way to convert the value to an int, so 3.4 becomes 3 (and
> and the 4/10's is lost).

Why is that a problem?  Loss is not the issue.  And as someone else 
pointed out, int('4') does not lose information, but seq['1'] is 
prohibited.  Why is passing integer strings as indexes bad?

The answer to the latter, I believe, is that Guido is against treating 
numbers and string representations of numbers as interchangable.  And 
the answer to both, I believe, is that the downside of flexibility is 
ease of creating buggy code, especially code where bugs do not 
immediately raise something, or ease of creating confusing code that is 
hard to maintain.

-- 
Terry Jan Reedy