decimal and context objects!

Peter Otten __peter__ at web.de
Fri Mar 2 11:34:49 CET 2007


MooMaster wrote:

> Hey guys, I'm trying to do some black magic voodoo and it's a little
> late, so forgive me if this question seems obvious or has been asked
> before. I tried doing a search on context objects and didn't find
> anything that popped out, and I'm too tired to keep digging.
> 
> I'm making a little program that is trying to do weird and sexy things
> by fully leveraging the power of all the built-in beauty of Python. I
> was trying to play around with the new features added into Python 2.5,
> and ran into an unexpected issue...check this out:
> 
>>>> moo = lambda x, y :
>>>> decimal.Context(3).sqrt(decimal.Context(3).power(x,2) +
>>>> decimal.Context(3).power(y,2)) moo
> <function <lambda> at 0x02CD0EB0>
>>>> row = [1,2,3,4,5]
>>>> weight_vector = .00556
>>>> moo(sum(row), weight_vector)
> Traceback (most recent call last):
>   File "<pyshell#5>", line 1, in <module>
>     moo(sum(row), weight_vector)
>   File "<pyshell#1>", line 1, in <lambda>
>     moo = lambda x, y :
> decimal.Context(3).sqrt(decimal.Context(3).power(x,2) +
> decimal.Context(3).power(y,2))
>   File "C:\Python25\lib\decimal.py", line 2662, in power
>     return a.__pow__(b, modulo, context=self)
> TypeError: wrapper __pow__ doesn't take keyword arguments
> 
> I have no idea what keyword argument is getting passed to __pow__,
> anyone know what's going on?

Weird implementation hacks distorting error messages :-)
Context.power() expects a Decimal instance as its first argument:

>>> from decimal import *
>>> ctx = getcontext()
>>> ctx.power(10, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.5/decimal.py", line 2662, in power
    return a.__pow__(b, modulo, context=self)
TypeError: wrapper __pow__ doesn't take keyword arguments
>>> ctx.power(Decimal("10"), 2)
Decimal("100")

Peter



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