[Python-Dev] PEP 515: Underscores in Numeric Literals

[Terry Reedy]

On 2/11/2016 2:45 AM, Georg Brandl wrote:

Thanks for grabbing this issue and moving it forward.  I will like being 
about to write or read 200_000_000 and be sure I an right without 
counting 0s.

> Based on the feedback so far, I have an easier rule in mind that I will base
> the next PEP revision on.  It's basically
>
> "One ore more underscores allowed anywhere after a digit or a base specifier."
>
> This preserves my preferred non-restrictive cases (0b_1111_0000, 1.5_j) and
> disallows more controversial versions like "1.5e_+_2".

I like both choices above.  I don't like trailing underscores for two 
reasons.

1. The stated purpose of adding '_'s is to visually separate.  Trailing 
underscores do not do that.  They serve no purpose.
2. Trailing _s are used to turn keywords (class) into identifiers 
(class_).  To me, 123_ mentally clashes with this usage.

If trailing _ is allowed, to simplify the implementation, I would like 
PEP 8, while on the subject, to say something like "While trailing _s on 
numbers are allowed, to simplify the implementation, they serve no 
purpose and are strongly discouraged".

-- 
Terry Jan Reedy