[Python-Dev] Example for PEP 343

[Bob Ippolito]

On May 17, 2005, at 11:39 PM, Guido van Rossum wrote:

> [Raymond Hettinger]
>
>> However, for a general purpose wrapper, it is preferable to make a
>> context copy and then restore the context after the enclosed is run.
>> That guards against the enclosed block making any unexpected context
>> changes.
>>
>
> (Although if people get in the habit of using the provided wrappers
> and the do-statement, there won't be any unexpected changes.)
>
>
>> Also, since the wrapper is intended to work like a try/finally, it  
>> will
>> make sure the context gets restored even if an exception is raised at
>> some unexpected point in the middle of the computation.
>>
>
> Yes, that's the point of the do-statement. :-
>
> Anyway, perhaps we should provide this most general template:
>
>   @do_template
>   def with_decimal_context():
>       oldctx = decimal.getcontext()
>       newctx = oldctx.copy()
>       decimal.setcontext(newctx)
>       yield newctx
>       decimal.setcontext(oldctx)
>
> To be used like this:
>
>   do with_decimal_context() as ctx:
>       ctx.prec += 2
>       # change other settings
>       # algorithm goes here

I have yet to use the decimal module much, so I may be completely off  
here.. but why not write it like this:

@do_template
def with_decimal_context():
     curctx = decimal.getcontext()
     oldctx = curctx.copy()
     yield curctx
     decimal.setcontext(oldctx)

Saves a line and a context set :)

-bob