[Python-Dev] cpython (3.2): Issue #14123: Explicitly mention that old style % string formatting has caveats

[Guido van Rossum]

On Sun, Feb 26, 2012 at 3:14 PM, Terry Reedy <tjreedy at udel.edu> wrote:
> On 2/26/2012 5:38 PM, Nick Coghlan wrote:
>>
>> Ah, thanks, I knew there was another term that had a new-style
>> counterpart: percent formatting vs brace formatting.
>
> Hooray!
> Exact parallel and value-neutral.

Can we stop it with the "political correctness" already? The old style
is best named printf-style formatting because that's the origin of the
format language, and there are many other programming languages that
support the same formatting language (with minor variations). I care
less about what we call the new style -- "new style" or "format
method" both work for me.

I also would like to suggest that, even if the reality is that we
can't deprecate it today, *eventually*, at *some* *distant* point in
the future we ought to start deprecating printf-style formatting -- it
really does have a couple of nasty traps that keep catching people
unawares. In the mean time it doesn't hurt to use terms that make
people ever so slightly uneasy with using the old style for new code,
while also committing to not throwing it out until Python 4 comes
around.

That said, for consistency's sake, if you add formatting code to an
existing module that uses the old style, please stick to the old
style. And to avoid disasters, also please don't go on a library-wide
rampage of wholesale conversions. The time to start using the new
formatting is when writing new modules or packages, or possibly when
doing a major refactoring/upgrade of an existing module or package.

One thing I'd like to see happening regardless is support for
new-style formatting in the logging module. It's a little tricky to
think how that would work, alas -- should this be a property of the
logger or of the call?

-- 
--Guido van Rossum (python.org/~guido)