How can I represent an infinite number in python? No matter which number you enter in the program, no number should be greater than this representation of infinity.
In Python, you can do:
test = float("inf")
In Python 3.5, you can do:
import math
test = math.inf
And then:
test > 1
test > 10000
test > x
Will always be true. Unless of course, as pointed out, x is also infinity or "nan" ("not a number").
Additionally (Python 2.x ONLY), in a comparison to Ellipsis, float(inf) is lesser, e.g:
float('inf') < Ellipsis
would return true.
Since Python 3.5 you can use math.inf:
>>> import math
>>> math.inf
inf
I don't know exactly what you are doing, but float("inf") gives you a float Infinity, which is greater than any other number.
No one seems to have mentioned about the negative infinity explicitly, so I think I should add it.
For positive infinity (just for the sake of completeness):
math.inf
For negative infinity:
-math.inf
Another, less convenient, way to do it is to use Decimal class:
from decimal import Decimal
pos_inf = Decimal('Infinity')
neg_inf = Decimal('-Infinity')
There is an infinity in the NumPy library: from numpy import inf. To get negative infinity one can simply write -inf.
In python2.x there was a dirty hack that served this purpose (NEVER use it unless absolutely necessary):
None < any integer < any string
Thus the check i < '' holds True for any integer i.
It has been reasonably deprecated in python3. Now such comparisons end up with
TypeError: unorderable types: str() < int()
Also if you use sympy you can use sympy.oo
>>> from sympy import oo
>>> oo + 1
oo
>>> oo - oo
nan
etc.
first of all type of float('inf') is float though it can be used for comparison purpose but it is considerably slow to compare against it. So if you are comparing a large list of number against float('inf') then be careful to pick it. I am not sure about the performance of "math.inf".
来源：https://stackoverflow.com/questions/7781260/how-can-i-represent-an-infinite-number-in-python