[Python-ideas] Python Float Update

Terry Reedy tjreedy at udel.edu
Tue Jun 2 19:29:14 CEST 2015

On 6/2/2015 9:05 AM, Andrew Barnert via Python-ideas wrote:

> OK, so what are the stumbling blocks to adding decimal32/64/128 (or
> just one of the three), either in builtins/stdtypes or in decimal,
> and then adding literals for them?

A compelling rationale.  Python exposes the two basic number types used 
by the kinds of computers it runs on: integers (extended) and floats 
(binary in practice, though the language definition would all a decimal 
float machine).

The first killer app for Python was scientific numerical computing.  The 
first numerical package developed for this exposed the entire gamut of 
integer and float types available in C.  Numpy is the third numerical 
package. (Even so, none of the packages have been distributed with 
CPython -- and properly so.)

Numbers pre-wrapped as dates, times, and datetimes with specialized 
methods are not essential (Python once managed without) but are 
enormously useful in a wide variety of application areas.

Decimals, another class of pre-wrapped numbers, greatly simplify money 
calculations, including those that must follow legal or contractual 
rules.  It is no accident that the decimal specification is a product of 
what was once International Business Machines. Contexts and specialized 
rounding rules are an essential part of fulfilling the purpose of the 

What application area would be opened up by adding a fixed-precision 
float?  The only thing I have seen presented is making interactive 
python act even more* like a generic (decimal) calculator, so that 
newbies will find python floats less surprising that those of other 
languages.  (Of course, a particular decimal## might not exactly any 
existing calculator.)

*The int division change solved the biggest discrepancy: 1/10 is not .1 
instead of 0. Representation changes improved things also.

Terry Jan Reedy

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