Hey all,

based on the feedback so far, I revised the PEP.  There is now
a much simpler rule for allowed underscores, with no exceptions.
This made the grammar simpler as well.

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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, floating-point and complex 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

    # making the literal suffix stand out more
    imag = 1.247812376e-15_j


Specification
=============

The current proposal is to allow one or more consecutive underscores following
digits and base specifiers in numeric literals.