How do I type a floating point infinity literal in python?
I have heard
inf = float('inf')
is non portable. Thus, I have had the following recommended:
inf = 1e400
Is either of these standard, or portable? What is best practice?
views:
185answers:
3
+10
A:
In python 2.6 it is portable if the CPU supports it
The float() function will now turn the string nan into an IEEE 754 Not A Number value, and +inf and -inf into positive or negative infinity. This works on any platform with IEEE 754 semantics.
Mark
2010-05-27 09:11:28
What happens on platforms without IEEE 754 semantics?
fmark
2010-05-27 09:15:14
@fmark: Good luck finding a platform that Python runs on but that doesn't have IEEE 754 semantics. In theory, `float('inf')` should raise `ValueError` on these platforms, but to my knowledge this behaviour has never been tested, because Python (well, recent versions of Python, at least) has yet to meet such a platform. In practice don't worry about it.
Mark Dickinson
2010-05-27 10:09:32
+2
A:
float('inf') is non portable as in not portable back to Python 2.5 when the string output varies between platforms. From 2.6 and onwards float('inf') is guaranteed to work on IEEE-754-compliance platforms (ref: http://www.python.org/dev/peps/pep-0754/).
(And the recommendation seems to be in the range 1e30000, not just 1e400.)
KennyTM
2010-05-27 09:13:13
+2
A:
Perhaps you could do somthing like this
try:
inf = float('inf')
except: # check for a particular exception here?
inf = 1e30000
gnibbler
2010-05-27 09:23:36
+1. `float('inf')` is definitely to be preferred, in general. It's even possible that 'inf = 1e30000` might start raising `OverflowError` instead of producing an infinity in some future version of Python.
Mark Dickinson
2010-05-27 10:06:59