[Python-Dev] PEP 0484 - the Numeric Tower

[Raymond Hettinger]

> On Oct 13, 2015, at 4:21 AM, Laura Creighton <lac at openend.se> wrote:
> 
> Any chance of adding Decimal to the list of things that are also
> acceptable for things annotated float?

From Lib/numbers.py:

## Notes on Decimal
## ----------------
## Decimal has all of the methods specified by the Real abc, but it should
## not be registered as a Real because decimals do not interoperate with
## binary floats (i.e.  Decimal('3.14') + 2.71828 is undefined).  But,
## abstract reals are expected to interoperate (i.e. R1 + R2 should be
## expected to work if R1 and R2 are both Reals).

That is still true:

Python 3.5.0 (v3.5.0:374f501f4567, Sep 12 2015, 11:00:19) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "copyright", "credits" or "license()" for more information.
>>> from decimal import Decimal
>>> Decimal('3.14') + 2.71828
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    Decimal('3.14') + 2.71828
TypeError: unsupported operand type(s) for +: 'decimal.Decimal' and 'float'


Raymond Hettinger