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

Steven D'Aprano steve-REMOVE-THIS at cybersource.com.au
Thu Aug 5 08:20:58 CEST 2010

On Wed, 04 Aug 2010 21:33:31 -0700, John Nagle 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])

What does the name "editmoney" mean? 

Why the obfuscated one-liner? It's not like you're using it in-line, 
you're putting it in a function, so who cares if it's one line or twenty?

def group_digits(n, size=3, sep=','):
    """Group int n in groups of size digits separated by sep."""
    s = str(n)
    m = len(s) % size
    head = s[0:m]
    tail = s[m:]
    groups = [tail[i*size:(i+1)*size] for i in range(len(tail)//size)]
    tail = sep.join(groups)
    if head and tail:
        return head + sep + tail
    elif tail:
        return tail
        return head

>>> group_digits(0)
>>> group_digits(1234567890)
>>> group_digits(1234567890, 4, ';')

Additional error checking, a better docstring, and extending it to 
support negative numbers is left as an exercise.


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