PEP 327: Decimal Data Type

[Dan Bishop]

Stephen Horne <steve at ninereeds.fsnet.co.uk> wrote in message news:<qeq520pv7kbd1s3ojmn3idetjuljhtk5md at 4ax.com>...
> On 5 Feb 2004 09:18:12 -0500, aahz at pythoncraft.com (Aahz) wrote:
> 
> >In article <ad052e5c.0401310101.1c5bd5aa at posting.google.com>,
> >Dan Bishop <danb_83 at yahoo.com> wrote:
> >>
> >>For money, it means that I have *exactly* $1.80.  This is because
> >>"dollars" are just a notational convention for large numbers of cents.
> >> I can just as accuately say that have an (integer) 180 cents, and
> >>indeed, that's exactly the way it would be stored in my financial
> >>institution's database.  (I know because I used to work there.)  So
> >>all you really need here is "int".  But I do agree with the idea of
> >>having a class to hide the decimal/integer conversion from the user.
> >
> >Really.  What kind of financial institution was this?  They didn't need
> >to deal with any form of fractional pennies?
> 
> Does it really matter if they did? They may not deal in whole pennies,
> but I seriously doubt that they need infinite precision - integers
> with a predefined scaling factor (ie fixed point arithmetic) will, I
> suspect, handle those few jobs that counting in pennies can't.

And you would be right.  For example, interest rates were always
stored in thousandths of a percent.

The only problem was that some of the third-party software we used
made this scaling completely visible to the user.  Our employees would
occasionally forget the scaling factor, and this resulted in mistakes
like having one of our CD's pay 445% interest instead of 4.45%.

> That said, as I understand it, a lot of financial institutions have a
> lot of COBOL code. And from what I remember of programming in COBOL,
> the typical representation of numbers in both files and working
> storage uses decimal digits stored in a character string - at least
> that's what the picture strings specify in the source code.

We had a lot of numbers in EBCDIC signed decimal.  Even though our
mainframe used ASCII.