[M.-A. Lemburg]
> Just out of curiosity: is there a usable decimal type implementation
> somewhere on the net which we could beat on ?
ftp://ftp.python.org/pub/python/
contrib-09-Dec-1999/DataStructures/FixedPoint.py
It's more than two years old, and regularly mentioned on c.l.py. From the
tail end of the module docstring:
"""
The following Python operators and functions accept FixedPoints in the
expected ways:
binary + - * / % divmod
with auto-coercion of other types to FixedPoint.
+ - % divmod of FixedPoints are always exact.
* / of FixedPoints may lose information to rounding, in
which case the result is the infinitely precise answer
rounded to the result's precision.
divmod(x, y) returns (q, r) where q is a long equal to
floor(x/y) as if x/y were computed to infinite precision,
and r is a FixedPoint equal to x - q * y; no information
is lost. Note that q has the sign of y, and abs(r) < abs(y).
unary -
== != < > <= >= cmp
min max
float int long (int and long truncate)
abs
str repr
hash
use as dict keys
use as boolean (e.g. "if some_FixedPoint:" -- true iff not zero)
"""
> I for one would be very interested in having a decimal type
> around (with fixed precision and scale),
FixedPoint is unbounded "to the left" of the point but maintains a fixed and
user-settable number of (decimal) digits "after the point". You can easily
subclass it to complain about overflow, or whatever other damn-fool thing you
think is needed <wink>.
> since databases rely on these a lot and I would like to assure
> that passing database data through Python doesn't cause any data
> loss due to rounding issues.
Define your ideal API and maybe I can implement it someday. My employer also
has use for this. FixedPoint.py is better suited to computation than I/O,
though, since it uses Python longs internally, and conversion between
BCD-like formats and Python longs is expensive.
> If there aren't any such implementations yet, the site that Tim
> mentioned looks like a good starting point for heading into this
> direction... e.g. for mx.Decimal ;-)
>
> http://www2.hursley.ibm.com/decimal/
FYI, note that Cowlishaw is moving away from REXX's "string of ASCII digits"
representation toward a variant of BCD encoding.
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