Mark Dickinson wrote:
But the Fraction type is going to mess this up: for Decimal + Fraction -> Decimal, I don't see any other sensible option than to convert the Fraction using the current context, since lossless conversion isn't generally possible.
You could convert the Decimal to a Fraction, do the arithmetic as Fractions, and convert the result back to Decimal using the current precision. I think this would satisfy the principle of performing the calculation as though infinite precision were available, and the final rounding is justified, since seen from the outside we are performing a single operation on two numbers. Another approach would be to convert the numerators and denominators separately to Decimal, and then do a/b + c/d = (a*d + b*c) / (b*d) using the usual rules of Decimal arithmetic. This would incur more than one rounding, but the rules for Decimals concern operations between two Decimals, and we have a Decimal and a Fraction here, so all bets could be considered off. -- Greg _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
