Splitting a string into substrings of equal size

[ryles]

On Aug 15, 6:28 pm, MRAB <pyt... at mrabarnett.plus.com> wrote:

> >      >>> for z in ["75096042068045", "509", "12024", "7", "2009"]:
> >            print re.sub(r"(?<=.)(?=(?:...)+$)", ",", z)
>
> >     75,096,042,068,045
> >     509
> >     12,024
> >     7
> >     2,009
>
> The call replaces a zero-width match with a comma, ie inserts a comma,
> if certain conditions are met:
>
> "(?<=.)"
>      Look behind for 1 character. There must be at least one previous
> character. This ensures that a comma is never inserted at the start of
> the string. I could also have used "(?<!^)". Actually, it doesn't check
> whether the first character is a "-". That's left as an exercise for the
> reader. :-)
>
> "(?=(?:...)+$)"
>      Look ahead for a multiple of 3 characters, followed by the end of
> the string.

Wow, well done. An exceptional recipe from Python's unofficial regex
guru. And thanks for sharing the explanation.