[Python-Dev] Re: Decimal data type issues

[Kevin Jacobs]

Batista, Facundo wrote:

>[Jewett, Jim J]
>#- Under the current implementation:
>#- 
>#- 	(0, (2, 4, 0, 0, 0), -4) 
>#- 
>#- is not quite the same as
>#- 
>#- 	(0, (2, 4) -1)
>#- 
>#- Given this, is should be possible for the user to specify 
>#- (at creation) which is desired.
>
>It *is* posible:
>  
>
>>>>Decimal('2.4000')
>>>>        
>>>>
>Decimal( (0, (2, 4, 0, 0, 0), -4) )
>  
>
>>>>Decimal('2.4')
>>>>        
>>>>
>Decimal( (0, (2, 4), -1) )
>  
>

<sarcasm>Great!</sarcasm>.   One of my previous posts specifically listed
that I didn't want to have to pre-parse and reformulate string literals to
achieve the desired precision and scale.  The "external" library solution
will either have to do that, or create a Decimal from the string literal,
look at the tuple length and exponent and form a new Decimal instance,
rounding if necessary.  Hmmm... sounds like something low-level
enough that Decimal should be doing it.  And remember, SQL and
many financial applications will be doing this operation for every
datum they load.

>#- I agree that the programmer should specify if they want 
>#- something odd -- and that is precisely why the constructor 
>#- should take an optional context argument which allows the 
>#- user to specify precision.
>
>If you construct using precision, and the precision is smaller than the
>quantity of digits you provide, you'll get rounded, but if the precision is
>greater than the quantity of digits you provide, you don't get filled with
>zeros.
>  
>

Rounding is exactly what should be done if one exceeds the desired 
precision.  Using
less that the desired precision (i.e., not filling in zeros) may be okay 
for many applications.
This is because any operations on the value will have to be performed 
with the precision
defined in the decimal context.  Thus, the results will be identical, 
other than that the
Decimal instance may not store the maximum precision available by the 
schema.

Thanks,
-Kevin