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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Delegation in Python
Date: Sat, 24 Jan 2015 20:31:31 -0500
References: <FeCdnXdsTpunvlnJnZ2dnUVZ8judnZ2d@brightview.co.uk>
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Xref: csiph.com comp.lang.python:84537

On 1/24/2015 5:57 PM, Brian Gladman wrote:
> I would appreciate advice on how to set up delgation in Python.
>
> I am continuously implementing a function to test whether a Python
> Fraction is an integer

Since Fractions are reduced to lowest terms,
 >>> from fractions import Fraction as F
 >>> F(4, 2)
Fraction(2, 1)
 >>> F(12, 3)
Fraction(4, 1)

the test is that the denominator is 1

 >>> F(12,3).denominator == 1
True
 >>> F(12,5).denominator == 1
False

it may not be worth the bother to define a function,

def fint(F): return F.denominator == 1

>so I wanted to define a new class, based on
> Fraction, that includes this new method.

but if you do, there is little need to make it a method.  You are not 
overriding an existing method or adding a new special method.  The math 
module has float and int functions that have *not* been turned into 
methods.  Ditto for cmath.  I would just leave the function a function. 
  Python is not Java.

-- 
Terry Jan Reedy