Tim Peters added the comment: Mark, these are the "spirit of 754" rules:
1. If the mathematical result is a real number, but of magnitude too large to approximate by a machine float, overflow is signaled and the result is an infinity (with the appropriate sign). 2. If the mathematical result is a real number, but of magnitude too small to approximate by a machine float, underflow is signaled and the result is a zero (with the appropriate sign). 3. At a singularity (a value x such that the limit of f(y) as y approaches x exists and is an infinity), "divide by zero" is signaled and the result is an infinity (with the appropriate sign). This is complicated a little by that the left-side and right-side limits may not be the same; e.g., 1/x approaches +inf or -inf as x approaches 0 from the positive or negative directions. In that specific case, the sign of the zero determines the result of 1/0. 4. At a point where a function has no defined result in the extended reals (i.e., the reals plus an infinity or two), invalid operation is signaled and a NaN is returned. And these are what Python has historically /tried/ to do (but not always successfully, as platform libm behavior varies a lot): For #1, raise OverflowError. For #2, return a zero (with the appropriate sign if that happens by accident ;-)). For #3 and #4, raise ValueError. It may have made sense to raise Python's ZeroDivisionError in #3, but historically that's only been raised for division by zero and mod by zero. You're right that you can't make everyone happy, so may as well stick with historical consistency, and wait for a PEP to introduce a more flexible mechanism. As W. Kahan wrote long ago, the reason they're called "exceptions" is that no matter which fixed policy you adopt, someone will take strident exception to it ;-) __________________________________ Tracker <[EMAIL PROTECTED]> <http://bugs.python.org/issue1640> __________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
