input: Write a function to slice a string in Python that takes a string, a start index, and an end index, and returns the substring from the start index to the end index.
  assert slicing("This is a slicing test", 8, 15)=="a slicing"
  assert slicing("Hello, world!", 7, 12)=="world"
  assert slicing("Python programming", 7, 18)=="programmin"
  assert slicing("Short string", 0, 5)=="Short"
  assert slicing("", 0, 0)==""
output: def slicing(s, start, end):
      return s[start:end]