input: Write a python function to convert all lowercase letters to uppercase and all uppercase letters to lowercase in a provided string.
  assert switch_case('') == ''
  assert switch_case('Hello!') == 'hELLO!'
  assert switch_case('These violent delights have violent ends') == 'tHESE VIOLENT DELIGHTS HAVE VIOLENT ENDS'
output: def switch_case(s):
      return s.swapcase()