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

[Barry Warsaw]

On Sep 29, 2009, at 11:15 PM, Martin v. Löwis wrote:

> I would propose that the format argument gets an argument name,
> according to the syntax it is written in. For PEP 3101 format,
> I would call the argument "format" (like the method name of the
> string type), i.e.
>
> logging.Formatter(
>  format="{asctime} - {name} - {levelname} - {message}")
>
> For the % formatting, I suggest "dicttemplate" (assuming that
> you *have* to use dictionary %(key)s style currently).
>
> 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.

If this is adopted, it should become a common idiom across Python so  
that once you've learned how to transition between the format strings,  
you pretty much know how to do it for any supporting API.  So we  
should adopt it across all of the standard library.

-Barry

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