A useful, but painful, one-liner to edit money amounts

[Rebel Lion]

On Aug 5, 12:33 pm, John Nagle <na... at animats.com> wrote:
> There's got to be a better way to do this:
>
> def editmoney(n) :
>      return((",".join(reduce(lambda lst, item : (lst + [item]) if
>          item else lst,
>          re.split(r'(\d\d\d)',str(n)[::-1]),[])))[::-1])
>
>  >>> editmoney(0)
> '0'
>  >>> editmoney(13535)
> '13,535'
>  >>> editmoney(-14535)
> '-14,535'
>  >>> editmoney(123456)
> '123,456'
>  >>> editmoney(1234567890)
> '1,234,567,890'
>  >>> editmoney(-1234)
> '-1,234'
>
> The basic idea here is that we want to split the string of digits
> into groups of 3 digits, aligned at the right.  Because regular
> expressions are right to left, we have to reverse the string to
> do that, then reverse again at the end.  s[::-1} reverses an
> interable.
>
> "split" with a capturing group introduces empty strings into the
> list.  Hence the "reduce" and lambda to get rid of them.
>
> Any better ideas?
>
> (Yes, I know there's a built-in feature for this scheduled for
> Python 2.7.)
>
>                                         John Nagle

In [1]: '{:,}'.format(-12345678)
Out[1]: '-12,345,678'