[Python-Dev] Symmetry arguments for API expansion

[Raymond Hettinger]

> On Mar 13, 2018, at 10:43 AM, Guido van Rossum <guido at python.org> wrote:
> 
> So let's make as_integer_ratio() the standard protocol for "how to make a Fraction out of a number that doesn't implement numbers.Rational". We already have two examples of this (float and Decimal) and perhaps numpy or the sometimes proposed fixed-width decimal type can benefit from it too. If this means we should add it to int, that's fine with me.

I would like that outcome.  

The signature x.as_integer_ratio() -> (int, int) is pleasant to work with.  The output is easy to explain, and the denominator isn't tied to powers of two or ten. Since Python ints are exact and unbounded, there isn't worry about range or rounding issues.

In contrast, math.frexp(float) ->(float, int) is a bit of pain because it still leaves you in the domain of floats rather than letting you decompose to more more basic types.  It's nice to have a way to move down the chain from ℚ, ℝ, or ℂ to the more basic ℤ (of course, that only works because floats and complex are implemented in a way that precludes exact irrationals).


Raymond