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

Raymond Hettinger python at rcn.com
Wed Sep 30 19:05:05 CEST 2009

[Terry Reedy]
> However it is done, I think someone (like new Python programmers) should 
> be able to program in Python3, and use everything in the stdlib, without 
> ever learning % formatting -- and that I should be able to forget about 
> it ;-).
> +10 on the goal.

If that were possible, it would be nice.  But as long as the language supports
%-formatting, it is going to be around in one form or another.   Any non-casual 
user will bump into %-formatting in books, in third-party modules, in ASPN recipes, 
on the newsgroup, and in our own source code.  If they maintain any exising
software, they will likely encounter too.  It doesn't seem to be a subject that
can be ignored.

Also, I think it premature to say that {}-formatting has been proven in battle.
AFAICT, there has been very little uptake.  I've personally made an effort
to use {}-formatting more often but find that I frequently have to lookup
the syntax and need to experiment with the interactive interpreter to get it right.
I haven't found it easy to teach or to get other people to convert.  This is
especially true if the person has encountered %-formatting in other languages
(it is a popular approach).


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