[Python-Dev] [Python-checkins] python/nondist/peps pep-0343.txt, 1.11, 1.12

[Tim Peters]

[Greg Ewing]
> I don't see it's because of that. Even if D(whatever)
> didn't ignore the context settings, you'd get the same
> oddity if the numbers came from somewhere else with a
> different precision.

Most users don't change context precision, and in that case there is
no operation defined in the standard that can _create_ a decimal "with
different precision".  Python's Decimal constructor, however, can
(Python's Decimal constructor performs an operation that's not in the
standard -- it's a Python-unique extension to the standard).

> I'm very uncomfortable about the whole idea of a
> context-dependent precision. It just seems to be
> asking for trouble.

If you're running on a Pentium box, you're using context-dependent
precision a few million times per second.  Most users will be as
blissfully unaware of decimal's context precsion as you are of the
Pentium FPU's context precision.  Most features in fp standards are
there for the benefit of experts.  You're not required to change
context; those who need such features need them desperately, and don't
care whether you think they should <wink>.

An alternative is a God-awful API that passes a context object
explicitly to every operation.  You can, e.g., kiss infix "+" goodbye
then.  Some implementations of the standard do exactly that.

You might want to read the standard before getting carried off by gut reactions:

    http://www2.hursley.ibm.com/decimal/