On Mar 8, 2014, at 13:01, "Mark H. Harris" <harrismh777@gmail.com> wrote:



On Saturday, March 8, 2014 2:16:00 PM UTC-6, Mark H. Harris wrote:


On Saturday, March 8, 2014 12:49:02 PM UTC-6, Mark Dickinson wrote:
 
- if we're aiming to eliminate surprises, the 'fix' doesn't go far enough: Decimal(1.1 + 2.2) will still surprise, as will {snip}

How about this then:   I think I've got it...

>>> ===== RESTART =========================
>>> from pdeclib import *
>>> d(1.1+2.2)
Decimal('3.3')
>>> sqrt(1.1+2.2)**2
Decimal('3.29999999999999999999999999999999999999999')
>>> x=d(1.1)
>>> y=d(2.2)
>>> sqrt(x+y)**2
Decimal('3.29999999999999999999999999999999999999999')
>>> 

Code Below--------------------------
 
#*****************************************************************/
# sqrt(x)    return decimal sqrt(x) rounded to context precision
#*****************************************************************/
def sqrt(x):
    """ sqrt(x)     square root function

             (x may be string, int, float, or decimal)
             (returns decimal rounded to context precision)
    """
    with localcontext(ctx=None) as cmngr:
        cmngr.prec+=14
        if (isinstance(x, float)==True):
            y=x.__round__(15)
            sqr=Decimal(repr(y)).sqrt()
        else:
            sqr=Decimal(x).sqrt()
    return +sqr

-------------------- what say you? ---------------------

It looks like you're trying to emulate a pocket calculator here. The question is, why are you accepting floats in the first place if that's your goal?