decimal and trunkating

[Peter Hansen]

Timothy Smith wrote:
> i want to trunkate 199.999 to 199.99
> getcontext.prec = 2 isn't what i'm after either, all that does is E's 
> the value.
> do i really have to use floats to do this?

I think you need a context with appropriate rounding set (e.g. 
ROUND_FLOOR?) and then use the quantize() method with an argument with 
the appropriate number of decimal places.

For example, this works, though I'm definitely not a Decimal expert and 
am confident there's a more elegant approach (which might depend on more 
information about what you're doing):

 >>> d = decimal.Decimal('199.999')
 >>> decimal.getcontext().rounding = decimal.ROUND_FLOOR
 >>> d.quantize(decimal.Decimal('1.00'))
Decimal("199.99")

-Peter

(I hope this inspires someone who actually knows what he's doing with 
Decimal to post an improved solution.)