[Python-Dev] [format] Restrict fill characters for numerical values

[Eric Smith]

Stefan Krah wrote:
> Hi,
> 
> I think http://www.python.org/dev/peps/pep-3101/ is too liberal with the
> choice of fill characters for numerical values. As far as I can see, this
> is quite legal:
> 
> 
> Python 2.7a0 (trunk:76132M, Nov  6 2009, 15:20:35) 
> [GCC 4.1.3 20080623 (prerelease) (Ubuntu 4.1.2-23ubuntu3)] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
>>>> from decimal import *
>>>> format(Decimal(4), "9<10")
> '4999999999'
>>>> format(Decimal(4), "9>10")
> '9999999994'
>>>> format(Decimal(4), "->2")
> '-4'
> 
> 
> I propose to disallow digits and '+-' fill characters for numerical values,
> except for the combination '0, left-padding'. Actually, I'd prefer to allow
> only whitespace and '0, left-padding'.

Why?

What problem are you trying to prevent that would justify the extra code 
to implement this and the extra documentation to explain it?

Eric.