[Python-ideas] new format spec for iterable types

Andrew Barnert abarnert at yahoo.com
Wed Sep 9 02:03:22 CEST 2015

On Sep 8, 2015, at 12:38, random832 at fastmail.us wrote:
>> On Tue, Sep 8, 2015, at 12:27, Stephen J. Turnbull wrote:
>> I'm afraid this won't work unless restricted to be the last
>> replacement field, where it just consumes all remaining positional
>> arguments.  I think that restriction deserves a loud "ugh", but maybe
>> it will give somebody a better idea.
> So, this is the second time in as many weeks that I've suggested a new
> !converter, but this seems like the place for it - have something like
> "!join" which "converts" [wraps] the argument in a class whose
> __format__ method knows how to join [and call __format__ on the
> individual members].
> So you could make a list of floating point numbers by "List: {0:,
> |.2f!join}".format([1.2, 3.4, 5.6])
> and it will simply call Joiner([1.2, 3.4, 5.6]).__format__(", |.2f")

I like this version. 

Even without the flexibility, just adding another hardcoded 'j' converter for iterables would be nice, but being able to program it would of course be better.

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