[Python-Dev] PEP 460 reboot (original) (raw)

Greg Ewing greg.ewing at canterbury.ac.nz
Mon Jan 13 22:02:52 CET 2014

Guido van Rossum wrote:

On Sun, Jan 12, 2014 at 5:27 PM, Ethan Furman <ethan at stoneleaf.us> wrote:

On 01/12/2014 04:47 PM, Guido van Rossum wrote:

b'%s' % 'x' == b"'x'" (i.e. the three-byte string containing an 'x' enclosed in single quotes) I'm not sure about the quotes. Would anyone ever actually want those in the byte stream? Perhaps not, but it's a hint that you should probably think about an encoding. It's symmetric with how '%s' % b'x' returns "b'x'". Think of it as payback time. :-)

If it's never useful, wouldn't it be better to raise an exception in this case?

That way, someone porting code from py2 that does this without appropriate modification will find out about the problem immediately, rather than have spurious quotes inserted into their binary data, which -- being binary data -- will likely go unnoticed until something else tries to read the data.

I don't think the rule against operations that work on all-but-one-type really applies here, because the mistake it's intended to catch is not an obscure corner case. If your program's logic includes interpolating strings into bytes objects, then you're going to be testing that.

-- Greg

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