[Python-Dev] Backporting PEP 3101 to 2.6

[M.-A. Lemburg]

On 2008-01-10 14:31, Eric Smith wrote:
> (I'm posting to python-dev, because this isn't strictly 3.0 related.
> Hopefully most people read it in addition to python-3000).
> 
> I'm working on backporting the changes I made for PEP 3101 (Advanced
> String Formatting) to the trunk, in order to meet the pre-PyCon release
> date for 2.6a1.
> 
> I have a few questions about how I should handle str/unicode.  3.0 was
> pretty easy, because everything was unicode.

Since this is a new feature, why bother with strings at all
(even in 2.6) ?

Use Unicode throughout and be done with it.

> 1: How should the builtin format() work?  It takes 2 parameters, an
> object o and a string s, and returns o.__format__(s).  If s is None, it
> returns o.__format__(empty_string).  In 3.0, the empty string is of
> course unicode.  For 2.6, should I use u'' or ''?
> 
> 
> 2: In 3.0, object.__format__() is essentially this:
> 
>     class object:
>         def __format__(self, format_spec):
>             return format(str(self), format_spec)
> 
>     In 2.6, I assume it should be the equivalent of:
> 
>     class object:
>         def __format__(self, format_spec):
>             if isinstance(format_spec, str):
>                 return format(str(self), format_spec)
>             elif isinstance(format_spec, unicode):
>                 return format(unicode(self), format_spec)
>             else:
>                 error
> 
>      Does that seem right?
> 
> 
> 3: Every overridden __format__() method is going to have to check for
> string or unicode, just like object.__format() does, and return either a
> string or unicode object, appropriately.  I don't see any way around
> this, but I'd like to hear any thoughts.  I guess there aren't all that
> many __format__ methods that will be implemented, so this might not be a
> big burden.  I'll of course implement the built in ones.
> 
> Thanks in advance for any insights.

-- 
Marc-Andre Lemburg
eGenix.com

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