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

Raymond Hettinger python at rcn.com
Wed Sep 30 18:36:53 CEST 2009

The positional parameter would also mean dicttemplate, and would be deprecated (eventually requiring a keyword-only parameter).

Although I hate the name 'dicttemplate', this seems like the best solution to me. Maybe it's good that 'dicttemplate' is so ugly though so that people will naturally prefer 'format' :). But I like this because there's not really any magic, it's explicit, and the decision is made by the coder at the call site. The implementation does not need to guess at all. Could you comment on what you think we should do when the parameter is not positional? As I mentioned upthread, in the case of logging.Formatter, it's already documented as taking the keyword parameter "fmt", so we'd have to use the name "fmt" for % formatting.

Unless there is a firm decision to switch to kill %-formatting across the board, I don't think anything should be done at all.

Creating Py3.x was all about removing cruft and clutter. I don't think it would be improved by adding two ways to do it for everything in the standard library. That is a lot of additional code, API expansion, and new testing, fatter docs, and extra maintenance, but giving us no new functionality.

Anytime we start hearing about newstyle/oldstyle combinations, I think a flag should go up. Anytime there is a proposal to make sweeping additions that do not add new capabilities, a flag should go up.

I understand the desire to have all formatting support both ways, but I don't think it is worth the costs. People never need both ways though they may have differing preferences about which one to use.

my-two-cents,

Raymond

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