Python 3 bytes formatting

As of Python 3.5, % formatting will work for bytes, too!

This was part of PEP 461, authored by Ethan Furman:

PEP: 461
Title: Adding % formatting to bytes and bytearray
Version: $Revision$
Last-Modified: $Date$
Author: Ethan Furman <ethan at stoneleaf.us>
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 2014-01-13
Python-Version: 3.5
Post-History: 2014-01-14, 2014-01-15, 2014-01-17, 2014-02-22, 2014-03-25,
               2014-03-27
Resolution:


Abstract
========

This PEP proposes adding % formatting operations similar to Python 2's ``str``
type to ``bytes`` and ``bytearray`` [1]_ [2]_.


Rationale
=========

While interpolation is usually thought of as a string operation, there are
cases where interpolation on ``bytes`` or ``bytearrays`` make sense, and the
work needed to make up for this missing functionality detracts from the overall
readability of the code.


Motivation
==========

With Python 3 and the split between ``str`` and ``bytes``, one small but
important area of programming became slightly more difficult, and much more
painful -- wire format protocols [3]_.

This area of programming is characterized by a mixture of binary data and
ASCII compatible segments of text (aka ASCII-encoded text).  Bringing back a
restricted %-interpolation for ``bytes`` and ``bytearray`` will aid both in
writing new wire format code, and in porting Python 2 wire format code.

Common use-cases include ``dbf`` and ``pdf`` file formats, ``email``
formats, and ``FTP`` and ``HTTP`` communications, among many others.

PEP 461 was accepted by Guido van Rossum on March 27, 2014:

Accepted. Congrats with marshalling yet another quite contentious discussion, and putting up with my last-minute block-headedness!

From this, we can obviously conclude that % is no longer scheduled for deprecation (as was announced with Python 3.1).

Interestingly .format() doesn't appear to be supported for byte-sequences; as you have demonstrated.

You could use .join() as suggested here: http://bugs.python.org/issue3982

b", ".join([b'1', b'2', b'3'])

There is a speed advantage associated with .join() over using .format() shown by the BDFL himself: http://bugs.python.org/msg180449

I found the %b working best in Python 3.6.2, it should work both for b"" and "":

print(b"Some stuff %b. Some other stuff" % my_byte_or_unicode_string)

Another way would be:

"{0}, {1}, {2}".format(1, 2, 3).encode()

Tested on IPython 1.1.0 & Python 3.2.3