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

[Glenn Linderman]

On 2/10/2016 2:20 PM, Georg Brandl wrote:
> This came up in python-ideas, and has met mostly positive comments,
> although the exact syntax rules are up for discussion.
>
> cheers,
> Georg
>
> --------------------------------------------------------------------------------
>
> PEP: 515
> Title: Underscores in Numeric Literals
> Version: $Revision$
> Last-Modified: $Date$
> Author: Georg Brandl
> Status: Draft
> Type: Standards Track
> Content-Type: text/x-rst
> Created: 10-Feb-2016
> Python-Version: 3.6
>
> Abstract and Rationale
> ======================
>
> This PEP proposes to extend Python's syntax so that underscores can be used in
> integral and floating-point number literals.
>
> This is a common feature of other modern languages, and can aid readability of
> long literals, or literals whose value should clearly separate into parts, such
> as bytes or words in hexadecimal notation.
>
> Examples::
>
>      # grouping decimal numbers by thousands
>      amount = 10_000_000.0
>
>      # grouping hexadecimal addresses by words
>      addr = 0xDEAD_BEEF
>
>      # grouping bits into bytes in a binary literal
>      flags = 0b_0011_1111_0100_1110

+1

You don't mention potential restrictions that decimal numbers should 
permit them only every three places, or hex ones only every 2 or 4, and 
your binary example mentions grouping into bytes, but actually groups 
into nybbles.

But such restrictions would be annoying: if it is useful to the coder to 
use them, that is fine. But different situation may find other 
placements more useful... particularly in binary, as it might want to 
match widths of various bitfields.

Adding that as a rejected consideration, with justifications, would be 
helpful.
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