Backporting float(“inf”) to Python 2.4 and 2.5

Question

I'm backporting my project from Python 2.6 to Python 2.4 and 2.5. In my project I used float("inf"), and now I find it is unavailable on Python 2.5. Is there a backport of it?

Answer 1

I created a backport, tested on Python 2.5+, can probably be easily made to work on Python 2.4:

https://github.com/cool-RR/GarlicSim/blob/master/garlicsim/garlicsim/general_misc/infinity.py

Answer 2

Spelling it either the long way or the short way works fine for me:

$ python2.4 -c "print float('inf')+200"
inf
$ python2.5 -c "print float('inf')+200"
inf
$ python2.5 -c "print float('infinity')+200"
inf
$ python2.4 -c "print float('infinity')+200"
inf

The -c flag means "execute the following arguments as a Python command."

PEP754 (which was rejected) does mention your issue about special IEEE-754 values. It suggests using something like 1e300000 to generate a floating point overflow and create inf, but it does note that this is ugly and not guaranteed to be portable.

Answer 3

You should be able to fake it up by giving Python a sufficiently large floating point constant instead. For instance:

>>> 1e100000
inf
>>> float('inf') == 1e1000000
True
>>> float('inf') == 2e1000000
True

Answer 4

The decimal module is available since Python 2.4 and supports positive or negative infinite decimals. It does not always behave like a float (eg. adding a decimal and a float is not supported) but does the right thing for comparison, which was good enough for me.

>>> decimal.Decimal('Infinity') > 1e300
True

Answer 5

Borrowing NumPy for a few lines:

import numpy as np

inf = float(np.inf)

Here, inf is a regular python float, so you don't need to bother with NumPy any further.