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?
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4 Answers
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.
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Mark Dickinson
@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.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.)
Comments
Perhaps you could do something like this
try: inf = float('inf') except: # check for a particular exception here? inf = 1e30000 
1 Comment
Mark Dickinson
+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.