Fascinating. As an experiment I replaced str with repr and it usually
works with float. Float is better then integer because allows
migrations from one decimal type to float and vice versa and allows
for expressions involving different field types without major errors.
The problem is that when it fails, it has major failures.
Everybody should be aware that there will be much bigger rounding
errors with type='decimal' on sqlite than with type='double'. With
double the rounding errors will be of the order of required decimal
precision, much bigger than double precision.
That is because is
>>> a = 0.3/3 # is float
>>> print str(a)[0:5]
0.1
while
>>> from decimal import Decimal
>>> b=Decimal(repr(a)[0:5])
>>> print b
0.099
Conversions like the one above are necessary step to get data in/out
of database.
The more I look into this the more I think we should not support it if
the database does not support it.
Massimo
On Nov 13, 9:27 pm, Jonathan Lundell <jlund...@pobox.com> wrote:
> On Nov 13, 2009, at 4:36 PM, Massimo Di Pierro wrote:
>
> > In theory double has 53 bits. Yet I tried and it does not seem to work
> > properly. It rounds to the cents. You may want to try the attached
> > files. Perhaps I am doing something wrong.
>
> I'm not advocating floating point; I think it's a pain, and if integer is
> working, that's better. But....
>
> >>> from decimal import *
> >>> b = Decimal("1234567891.987654321")
> >>> b
>
> Decimal('1234567891.987654321')>>> float(b)
> 1234567891.9876542
> >>> str(float(b))
> '1234567891.99'
> >>> repr(float(b))
>
> '1234567891.9876542'
>
> I haven't checked, but it looks like an artifact of float.str.
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