Negation in regular expressions

[Ant]

> >>> re.split(r'@#', s)
> ['', ' This ', ' is a ', '', ' test ']
> >>> [g.group(1) for g in re.finditer(r'(.*?)(?:@#|$)', s)]
> ['', ' This ', ' is a ', '', ' test ', '']

If it's duplicating the behaviour of split, but returning an iterator
instead, how about avoiding hacking around with messy regexes and use
something like the following generator:

def splititer(pattern, string):
    posn = 0
    while True:
      m = pattern.search(string, posn)
      if not m:
        break
      yield string[posn:m.start()]
      posn = m.end()