We found some strange behavior of the handling of "nan" if "nan" is used in if-statements. We use Python 2.2 (python2-2.2.2-11.7.3.src.rpm). In the following i show the results of the "experiments" with "nan", "inf" and usual floats: $ python Python 2.2.2 (#1, Jan 30 2003, 21:26:22) [GCC 2.96 20000731 (Red Hat Linux 7.3 2.96-112)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> a=float(1.2345) >>> b=float("inf") >>> c=float("nan") >>> if a==b: ... print "equal" ... >>> if a==c: ... print "equal" ... equal >>> if b==c: ... print "equal" ... equal Bernhard Seiwald seiwald@itp.tugraz.at
Logged In: YES user_id=31435 Sorry, but all behavior in the presence of NaNs and infinities and signed zeroes is a platform- and release- dependent accident. Even that float("inf") didn't raise an exception for you is an accident (e.g., in Python 2.2.2 on Windows, it does raise an exception). I've added this to PEP 42's "non-accidental 754 support" feature request; you may also be interested in PEP 754 (support for 754 special values). Python has no 754 story now. If you want it to have one, consider volunteering work toward that end.
For the benefit of those who stumble here through Google, here's a workaround I've discovered for NaN testing. This is BAD: value == float('NaN') But this seems to work ok: str(value) == str(float('NaN'))
