[Python-Dev] Re: Decimal data type issues

[Jewett, Jim J]

Kevin Jacobs:
#-   Decimal('2.4000', precision=2, scale=1) == Decimal('2.4')
#-   Decimal('2.4', precision=5, scale=4) == Decimal('2.4000')
#- 
#- Remember, these literals are frequently coming from an 
#- external source that must be constrained to a given schema.

Facundo Batista:

> I like it a lot, but not for Decimal.

This is another face of "what to do with float"

Even if your default context is n digits, there is no reason
to assume that all your inputs will be measured that precisely.
If someone sends me a list of weights:

	PartA	1105 kg
	PartB	   3 kg

then I don't want to pretend that the 3kg part was weighed
any more precisely just because the total is smaller.

On the other hand, if the weights are:

	PartA	3 kg
	PartB 3.0 kg

then I do want to assume that the second weight is more precise.

As an example

	3000 g	3001 g
	+  2 g	+  1 g
      ------      ------
	   3kg	3002 g

#- I assume that a new Decimal would normally be created
#- with as much precision as the context would need for 
#- calculations.  By passing a context/precision/position,
#- the user is saying "yeah, but this measurement wasn't
#- that precise in the first place.  Use zeros for the
#- rest, no matter what this number claims."

I don't get to understand you, and I'm not sure if you have the right
concept. Several examples may help:

>>> getcontext().prec = 5
>>> Decimal(124)
Decimal( (0, (1, 2, 4), 0) )
>>> +Decimal(124)
Decimal( (0, (1, 2, 4), 0) )
>>> Decimal('258547.368')
Decimal( (0, (2, 5, 8, 5, 4, 7, 3, 6, 8), -3) )
>>> +Decimal('258547.368')
Decimal( (0, (2, 5, 8, 5, 5), 1L) )
>>> Decimal.from_float(1.1)
Decimal( (0, (1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 1,
7, 8, 4, 1, 9, 7, 0, 0, 1, 2, 5, 2, 3, 2, 3, 3, 8, 9, 0, 5, 3, 3, 4, 4, 7,
2, 6, 5, 6, 2, 5), -51L) )
>>> +Decimal.from_float(1.1)
Decimal( (0, (1, 1, 0, 0, 0), -4L) )

.	Facundo