[Python-Dev] Re: Decimal data type issues (original) (raw)

Casey Duncan casey at zope.com
Fri Apr 16 09:36:05 EDT 2004

On Fri, 16 Apr 2004 00:17:24 -0400 "Tim Peters" <tim_one at email.msn.com> wrote:

[Facundo Batista, on whether to limit exponent magnitude] [..] No, I want to spell the spec's mandatory from-string operation (which does use and affect context, in the specified ways) via an optional bool argument to the Decimal constructor. This isn't at all useless, although if you're only thinking about a money type it may seem that way. In general number-crunching, literals may be given to high precision, but that precision isn't free and usually isn't needed: the operations in the spec don't round back inputs to current context precision before computing, they only round outputs after, and digits feeding into computation are expensive. So, in general, a scientific user will usually not want all the digits in

pi = Decimal("3.1415926535897932384626433832795", usecontext=True) to be used. Instead they'll want to set the working precision once in context, and have their literals automatically get rounded back to that precision. [..]

I find boolean arguments a general anti-pattern, especially given we have class methods. Why not use an alternate constructor like::

pi = Decimal.rounded_to_context("3.1415926535897932384626433832795")

Spelling notwithstanding.

-Casey

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