Rappresenting infinite

[avassalotti at gmail.com]

On Jun 27, 6:41 am, andrea <kerny... at gmail.com> wrote:
> I would like to have a useful rappresentation of infinite, is there
> already something??
>
> I was thinking to something like this
>
> class Inf(int):
>         """numero infinito"""
>         def __init__(self,negative=False):
>                 self.negative = negative
>         def __cmp__(self,y):
>                 """infinito maggiore di qualasiasi cosa"""
>                 if self.negative:
>                         return -1
>                 else:
>                         return 1
>         def __repr__(self):
>                 """docstring for __repr__"""
>                 if self.negative:
>                         return '-inf'
>                 else:
>                         return 'inf'
>         def __add__(self,y):
>                 """addizione con infinito"""
>                 return self
>         def __mul__(self,y):
>                 """moltiplicazione"""
>                 import types
>                 if isinstance(y,types.IntType):
>                         if y > 0:
>                                 return self
>                         if y == 0:
>                                 return 'indefinito'
>                         else:
>                                 return Inf(negative)
>
> I'd like to be able to compare between any value and infinite always
> getting the right result, and paying attention to the special cases
> like
> inf / inf => not determinate

float('inf') works well, no?

   >>> inf = float('inf')
   >>> inf / inf
   nan
   >>> -inf
   -inf
   >>> inf / 0
   ZeroDivisionError: float division
   >>> 1 / inf
   0.0
   >>> 0 * float('inf')
   nan