[Python-Dev] PEP 460: allowing %d and %f and mojibake

Paul Moore p.f.moore at gmail.com
Sun Jan 12 18:26:15 CET 2014

On 12 January 2014 17:03, Ethan Furman <ethan at stoneleaf.us> wrote:
> We know full well the difference between unicode and bytes, and we know full
> well that numbers and much of the text we need has an ASCII (bytes!)
> representation.  When we do a b'Content Length: %d' % len(binary_data) we
> are expecting to get back a bytes object, /not/ a unicode object.

What I am struggling to understand here is what room for compromise
there is. Clearly, for whatever reason,

b'Content Length: ' + str(len(binary_data)).encode('ascii'))

is not acceptable for you. OK, fair enough. Also, apparently, writing a helper

def int_to_bytes(n):
    return str(n).encode('ascii')

b'Content Length: ' + int_to_bytes(len(binary_data))

is unacceptable. But I'm not clear why it's unacceptable. Maybe I
missed the explanation - God knows, the thread is long enough :-)

On the other hand, Nick has explained why b'Content Length: %d' %
len(binary_data) is unacceptable to him (you don't have to agree with
his opinion, just concede that he has explained his position in a way
that you understand).

I'm not trying to argue you're wrong - I don't know your codebase, nor
do I know your application area. But surely somewhere between "we must
have % formatting including %d for bytes" and the above, there's a
middle ground that you *are* willing to accept? Can you give any
indications of what that might be? What, specifically, about the
helper function is the problem? I don't think it is any less space
efficient, it doesn't double-encode, and I don't think it's more
difficult to understand (although it is a little longer, it trades
that off against being a bit more explicit as to what's going on).
Surely you're not arguing that your code must work unchanged (not
"there's a way of writing the code so it works on Python 2 and 3", but
"the code you currently have for Python 2 must work with no changes at

Can you give an example of code that is *nearly* acceptable to you,
which works in Python 2 and 3 today, and explain what improvements you
would like to see to it in order to use it instead of waiting for a
core change?


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