[issue2486] Consider using bytes type instead of str to store Decimal coefficients

[Mark Dickinson]

New submission from Mark Dickinson <dickinsm at gmail.com>:

The Python 3.0 version of decimal.py currently stores the coefficient of
a Decimal number (or the payload of a NaN) as a string, all of whose
characters are in the range '0' through '9'.

It may be more time-efficient to store the coefficient as a bytes 
instance instead, since bytes -> int conversion is likely to be faster 
than str -> int conversion.  On the other hand, int -> bytes conversion 
has to go through str, so may be significantly slower than int -> str 
conversion...

Bottom line:  this needs testing.

One other option:  it may even be worth considering storing the 
coefficient directly as a Python integer.  I've argued against this 
before, on the basis that it makes direct access to the decimal digits 
of a number harder, and this direct access is useful for rounding as 
well as for some of the more esoteric Decimal operations (logical 
operations, shifts and rotations).  But it may be worth a look.

(I think it's clear what the *right* option is, given unlimited 
developer time and energy:  decimal.py should represent the coefficient 
using a long integer implementation written in C, with wordsize a power 
of 10---probably either 10**4 or 10**9.)

See related discussion at issue 2482 and at

http://mail.python.org/pipermail/python-dev/2008-March/078189.html

----------
components: Library (Lib)
messages: 64521
nosy: facundobatista, marketdickinson, ncoghlan
severity: normal
status: open
title: Consider using bytes type instead of str to store Decimal coefficients
type: performance
versions: Python 3.0

__________________________________
Tracker <report at bugs.python.org>
<http://bugs.python.org/issue2486>
__________________________________