[Python-Dev] Decimal(unicode)

[Mark Dickinson]

On Tue, Mar 25, 2008 at 11:29 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> I thought that might be what happened, but I couldn't remember if that
> optimisation was a 2.6 only change or not (I suspect it was included in
> 2.5 as a prereq to the spec compliance updates).
>

Exactly.


> Anyway, +1 on coercing the mantissa to a str() instance in 2.5.
>
> This does raise an interesting point though - currently Decimal in Py3k
> is storing the mantissa as a Unicode instance instead of a bytes
> instance. The performance implications of that are horrendous since
> PyLong_FromUnicode does a malloc, encodes the string into the malloced
> buffer, then invokes PyLong_FromString on the result.
>

Urk!  Yes, this definitely needs to be looked at.


> The following is also a problem in Py3k:
> [...]
>
> The isinstance(value, str) check in Py3k is too restrictive - it needs
> to accept bytes instances as well.
>

I don't understand this. Why does Decimal.__new__ need to accept
bytes instances?  Isn't it just supposed to be creating a Decimal
from a string?  Or is the idea that it should accept ASCII strings
that are masquerading as bytes instances, for reasons of
convenience/efficiency/something else?

Unicode/bytes/str and encoding issues frighten me much more than
floating-point arithmetic ever did, so I expect I'm missing many
things here.

Mark
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