[Python-Dev] Tuples vs. lists (original) (raw)

Aahz Maruch aahz@rahul.net
Tue, 5 Feb 2002 10:03:13 -0800 (PST)

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.

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