[Python-Dev] transitioning from % to {} formatting (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Thu Oct 1 12:48:44 CEST 2009

Vinay Sajip <vinay_sajip yahoo.co.uk> writes:

This seems perhaps usable for a Formatter instantiation (infrequent) but a problem for the case where you want to convert formatstr + args -> message (potentially frequent, and less readable).

Why is it a problem? I don't understand. It certainly is less pleasant to write "{foo}".format or "{0} {1}".format than it is to write "{0} {1}" alone, but it's still prettier and easier to remember than the special wrappers people are proposing here.

Another problem is that logging calls already use keyword arguments (extra, excinfo) and so backward compatibility might be compromised.

Then logging can just keep recognizing those special keyword arguments, and forward the others to the formatting function.

It also feels like passing a callable could encourage patterns of usage which restrict our flexibility for future changes:

Which future changes are you thinking about? AFAIK, there hasn't been a single change in logging output formatting in years. Rejecting a present change on the basis that it "restricts our flexibility for future changes" sounds like the worst kind of argument to me :-)

That's more flexible, to be sure, but more specialized formatting requirements are already catered for using e.g. the PercentMessage/BraceMessage approach.

Except that having to wrap format strings with "PercentMessage" or "BraceMessage" is horrible. Python is not Java.

Regards

Antoine.

More information about the Python-Dev mailing list