[Python-Dev] Tuples vs. lists

[Aahz Maruch]

M.-A. Lemburg wrote:
> Aahz Maruch wrote:
>> M.-A. Lemburg wrote:
>>>
>>> For the BCD stuff Aahz was talking about, I'd suggest to have
>>> a look at either arrays or cStringIO buffers.
>> 
>> cStringIO wouldn't work because I want to store ints.  
> 
> I was thinking of storing integers as chr(value) in these.

Why spend the conversion time?

>> Arrays might
>> work, but I think I'll stick with tuples because they're a bit more
>> familiar to most Pythonistas.  I'm not too concerned with raw speed and
>> efficiency before I convert the code to C; remember Knuth.
> 
> If you plan to convert this to C, why not have a look at mxNumber
> first ? It's a wrapper around GMP and provides high performance
> implementations for many numeric operations, e.g. it should be easy
> to create a BCD type using the GMP (arbitrary length) longs and an
> additional C long for the decimal point position.  In fact, there's a
> GMP extension MPFR which tries to do just this.

I'm specifically implementing the ANSI BCD spec.  If you want to argue
the theory of this, poke the Timbot; I think it's simpler to ensure that
I'm following the spec if I implement everything by hand.  Once I really
understand what I'm doing, *then* it's time to optimize.

Note that one reason for using BCD over GMP longs (which are presumably
similar to Python longs) is speed of I/O conversion.
-- 
                      --- Aahz (@pobox.com)

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