generate imap message ranges from a list of ints

gistfile1.py

  msgRanges = []
  num = iter(sorted(numbers))
  startNum = None
  lastNum = None
  try:
    while True:
      curNum = num.next()
      if startNum is None:
        startNum = curNum
        lastNum = curNum
        continue
      if lastNum < curNum-1:
        if startNum == curNum:
          msgRanges.append("%d"%(startNum))
        else:
          msgRanges.append("%d:%d"%(startNum, lastNum))
        startNum = None
      lastNum = curNum
  except StopIteration:
    pass