[Python-ideas] Python Float Update

[Andrew Barnert]

On Jun 2, 2015, at 05:34, Nick Coghlan <ncoghlan at gmail.com> wrote:
> 
> This is one of the other
> main reasons why decimal64 or decimal128 are better candidates for a
> builtin decimal type than decimal.Decimal as it exists today (as well
> as being potentially more amenable to hardware acceleration on some
> platforms).

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?

I can imagine a few: someone has to work out exactly what features to support (the same things as float, or everything in the standard?), how it interacts with Decimal and float (which is defined by the standard, but translating that to Python isn't quite trivial), how it fits into the numeric tower ABCs, and what syntax to use for the literals, and if/how it fits into things like array/struct/ctypes and into math, and whether we need decimal complex values, and what the C API looks like (it would be nice if PyDecimal64_AsDecimal64 worked as expected on C11 platforms, but you could still use decimal64 on C90 platforms and just not get such functions...); then write a PEP; then write an implementation; and after all that work, the result may be seen as too much extra complexity (either in the language or in the implementation) for the benefits. But is that it, or is there even more that I'm missing?

(Of course while we're at it, it would be nice to have arbitrary-precision IEEE binary floats as well, modeled on the decimal module, and to add all the missing 754-2008/C11 methods/math functions for the existing float type, but those seem like separate proposals from fixed-precision decimal floats.)