On Mon, 22 Mar 2010 08:47:53 am Greg Ewing wrote:
Nick Coghlan wrote:
That's fine - binary floats *are* surprising. That's why Decimal exists in the first place.
This argument could equally well be used the other way -- someone using Decimal is doing so precisely because they *don't* want to be surprised, in which case they would probably prefer to get an exception.
Then they're in for a terrible, terrible disappointment. Rounding issues don't go away because you're using Decimal instead of float, and I can't imagine anyone would like an exception in the following cases:
Decimal(1)/Decimal(3)*Decimal(3) == Decimal(1) False Decimal(2).sqrt()**Decimal(2) == Decimal(2) False Decimal(10**28)+Decimal(1)-Decimal(10**28) == Decimal(1) False
Rounding isn't the only surprise:
x = Decimal("NAN"); x == x False
Decimals are floats, but using radix 10 instead of radix 2. -- Steven D'Aprano