[Python-ideas] Python Numbers as Human Concept Decimal System

[Steven D'Aprano]

On Mon, Mar 10, 2014 at 02:05:22PM +0000, Oscar Benjamin wrote:

> This is what I've been thinking about. Most non-expert users will be
> very happy with Decimal64 and a single fixed context. There could be a
> separate type called decimal64 in builtins that always used the same
> standard context. Literals could create decimal64 instances.
> 
> The semantics of code that uses this type and decimal literals would
> be independent of any arithmetic context which is good not just for
> constant folding but for understanding. There would be no need to
> explain what an arithmetic context is to new users. You can just say:
> "here's a type that represents decimal values with 16 digits. It
> sometimes needs to round if the result of a calculation exceeds 16
> digits so it uses the standard decimal rounding mode XXX."

All this sounds quite good to me. What's the catch? :-)


> Where this would get complicated is for people who also use the
> Decimal type. They'd need to keep track of which objects were of which
> type and so decimal literals might seem more annoying than useful.

Hmmm. I don't think this should necessarily be complicated, or at least 
no more complicated than dealing with any other mixed numeric types. If 
you don't want to mix them, don't mix them :-) 

(Perhaps there could be a Decimal context flag to allow/disallow mixed 
Decimal/decimal64 operations?)

I would expect that decimal64 and decimal.Decimal would be separate 
types. They might share parts of the implementation under the hood, but 
I don't think it would be necessary or useful to have decimal64 inherit 
from Decimal, or visa versa.


-- 
Steven