[Python-Dev] Mixing float and Decimal -- thread reboot (original) (raw)

Raymond Hettinger raymond.hettinger at gmail.com
Sun Mar 21 19:31:06 CET 2010

On Mar 20, 2010, at 9:40 PM, Greg Ewing wrote:

Mark Dickinson wrote:

Except that float is fixed-width (typically 53 bits of precision), while Decimal allows a user-specified, arbitrarily large, precision; Yes, but it still has some fixed limit at any given moment, so the result of an operation on Decimals always has the potential to produce an inexact result. It's not like an int or Fraction where the result can expand to whatever size is needed.

I'm thinking that I need to do more work on the Decimal documentation. There still seems to be a profound misunderstanding of its capabilities (i.e. that an Inexact flag can be set to preclude any inexact operations, that the precision can be automatically extended as needed during a calculation, or that many types of calculations can be done exactly especially if floor division is used). If rounded is needed, it can be controlled explicitly.

Raymond

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