> As to the implementation, the OS supplied float formatting does not add
> thousands separators.  I added the function add_thousands_grouping() to
> Python/pystrtod.c in order implement this for floats.

Excellent!  I didn't realise this code was already there.  Maybe there's 
also some way to use it to implement 'n' formatting for Decimal (which in 
some ways behaves like a hybrid floating-point and integer type).

I can't think of any reason that the LC_NUMERIC stuff shouldn't apply to 
integers as well as floats.