Rough draft: Proposed format specifier for a thousands separator

[MRAB]

Rhodri James wrote:
> On Mon, 16 Mar 2009 02:36:43 -0000, MRAB <google at mrabarnett.plus.com> 
> wrote:
> 
>> The field name can be an integer or an identifier, so the locale could
>> be too, provided that you know where to look it up!
>>
>>      financial = Locale(group_sep=",", grouping=[3])
>>      print("my number is {0:10n:{fin}}".format(1234567, fin=financial))
>>
>> Then again, shouldn't that be:
>>
>>      fin = Locale(group_sep=",", grouping=[3])
>>      print("my number is {0:{fin}}".format(1234567, fin=financial))
> 
> Except that loses you the format, since the locale itself is a collection
> of parameters the format uses.  The locale knows how to do groupings, but
> not whether to do them, nor what the field width should be.  Come to think
> of it, it doesn't know whether to use the LC_NUMERIC grouping information
> or the LC_MONETARY grouping information.  Hmm.
> 
> I can't believe I'm even suggesting this, but how about:
> 
>   print("my number is {fin.format("10d", {0}, True)}".format(1235467, 
> fin=financial))
> 
> assuming the locale.format() method remains unchanged?  That's horrible,
> and I'm pretty sure it can't be right, but I'm too tired to think of
> anything more sensible right now.
> 
It should probably(?) be:

     financial = Locale(group_sep=",", grouping=[3])
     print("my number is {0:10n:fin}".format(1234567, fin=financial))

The format "10n" says whether to use separators or a decimal point; the
locale "fin" says what the separator and the decimal point look like.