[Python-Dev] Issue 6081: format string using mapping rather than kwargs (original) (raw)

Eric Smith eric at trueblade.com
Thu Mar 25 13:57:00 CET 2010

Nick Coghlan wrote:

Filip Gruszczyński wrote:

I would appreciate any advice on this topic, even if this ticket would be dismissed altogether, as I would like to learn as much as possible on practices on developing Python. Raymond's use case is valid, but the currently proposed method name is way too long to be usable and the use of *args is a definite misfeature. I suggest approaching the issue with the exact spec needed to cover the problem Raymond described: Add a method to strings that allows a format string to be applied to an existing mapping without implicitly converting the mapping to a dict first.

It occurs to me that Raymond's use case could be satisfied using existing Python, by slightly changing the format string. After all, str.format() supports mapping lookup already:

$ ./python.exe Python 2.6.5+ (release26-maint:79421, Mar 25 2010, 08:51:39) [GCC 4.2.1 (Apple Inc. build 5646) (dot 1)] on darwin Type "help", "copyright", "credits" or "license" for more information.

class Default(dict): ... def missing(self, key): ... return key ... s = '{m[name]} was born in {m[country]}' s.format(m=Default(name='Guido')) 'Guido was born in country'

Considering that, maybe the best thing is to do nothing. I'll update the issue with this note.

-- Eric.

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