[Python-Dev] Example for PEP 343

[Guido van Rossum]

What's the advantage of using two calls to getcontext() vs. saving the
context in a local variable?

On 5/17/05, Raymond Hettinger <python at rcn.com> wrote:
> 
> 
> > -----Original Message-----
> > From: python-dev-bounces+python=rcn.com at python.org [mailto:python-dev-
> > bounces+python=rcn.com at python.org] On Behalf Of Phillip J. Eby
> > Sent: Tuesday, May 17, 2005 6:06 PM
> > To: Michael Chermside; gvanrossum at gmail.com
> > Cc: python-dev at python.org
> > Subject: Re: [Python-Dev] Example for PEP 343
> >
> > At 02:42 PM 5/17/2005 -0700, Michael Chermside wrote:
> >
> > ># ===== SAMPLE #1: increasing precision during a sub-calculation
> =====
> > >
> > >import decimal
> > >
> > >@do_template
> > >def with_extra_precision(places=2):
> > >     "Performs nested computation with extra digits of precision."
> > >     decimal.getcontext().prec += 2
> > >     yield None
> > >     decimal.getcontext().prec -= 2
> >
> > Won't this do the wrong thing if something within the block alters the
> > precision?
> 
> Right.
> 
> It should save, alter, and then restore:
> 
>    oldprec = decimal.getcontext().prec
>    decimal.getcontext().prec += 2
>    yield None
>    decimal.getcontext().prec = oldprec
> 
> 
> Raymond Hettinger
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-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)