How to represent the infinite ?

[Steve Tregidgo]

Cliff Wells <logiplexsoftware at earthlink.net> wrote in message news:<mailman.1024600723.6989.python-list at python.org>...
> from __future__ import generators
> 
> class Infinity(int):
>     def __init__(self):
>         int.__init__(self)
>         self.sign = 1
> 
>     def __str__(self):
>         return "%sInfinity" % {-1: "-", 1: ""}[self.sign]
> 
>     def __repr__(self):
>         return "<%s>" % self
[followed by many other good things]

Nice implementation.  May I suggest two small changes:

    def __init__(self, sign=1):
        int.__init__(self)
        self.sign = sign

    def __repr__(self):
        return "%s(%s)" % (self.__class__.__name__, self.sign)

It's partially tested (my version of Python doesn't have generators...
I really should get with the times); the point is that, assuming
Infinity is available in the calling namespace, this will work:

Python 1.5.2 (#0, Apr 13 1999, 10:51:12) [MSC 32 bit (Intel)] on win32
Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
>>> from some_module import Infinity
>>> i = Infinity()
>>> repr(i)
'Infinity(1)'
>>> j = eval(repr(i))
>>> j == i
1
>>> k = -eval(repr(i))
>>> k + i
0
>>> ^Z

Quoting from the Python reference manual (section 3.3.1):
> If at all possible, this should look like a valid Python expression
> that could be used to recreate an object with the same value (given
> an appropriate environment).

I'd be interested to hear if these minor modifications work with the
class proper; I had to remove the generator/yield lines, and the
subclassing from int, to get it to run under 1.5.2 :-)

Anyway, as I said: I like the class.

just-wanted-to-join-in-ly y'rs,
Steve

-- 
Steve Tregidgo