[Python-Dev] summary of transitioning from % to {} formatting

[Paul Moore]

2009/10/3 Antoine Pitrou <solipsis at pitrou.net>:
> Steven Bethard <steven.bethard <at> gmail.com> writes:
>>
>>   If %-formatting is to be deprecated, the transition strategy here
>>   is trivial. However, no one has yet written translators, and it is
>>   not clear what heuristics should be used, e.g. should the method
>>   just try %-formatting first and then {}-formatting if it fails?
>
> This would be a reasonable heuristic. It should be done only on the first call,
> though, and then the result remembered (for both performance reasons and
> consistency).
>
> The cases where a format string would function in both formatting styles and
> expect the same parameters must be very rare in the real world.

Define "fails":

>>> "{a} {b} c" % {'a':12}
'{a} {b} c'

That didn't fail...

Paul.