input: Write a Python function to parse slices from strings with single or range values.
  assert parseSlice("3") == slice(2, 3)
  assert parseSlice("1-5") == slice(0, 5)
  assert parseSlice("10-12") == slice(9, 12)
output: def parseSlice(s):
      if '-' in s:
          start, end = map(int, s.split('-'))
          return slice(start - 1, end)
      else:
          index = int(s)
          return slice(index - 1, index)