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

[Barry Warsaw]

On Sep 30, 2009, at 11:22 AM, Steven Bethard wrote:

> On Wed, Sep 30, 2009 at 5:21 AM, Barry Warsaw <barry at python.org>  
> wrote:
>> 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.
>
> 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.

I'm okay with fmt==%-formatting and format=={}-formatting, but I'd  
also be okay with transitioning 'fmt' to 'dicttemplate' or whatever.   
I think the important thing is to be explicit in the method signature  
which one you want (secondary would be trying to standardize this  
across the stdlib).

-Barry

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