input: Write a function to swap the values of two variables. The function should take two parameters and return the swapped values as a tuple. If either of the variables is None, return None.
  assert swap_values(5, 10)==(10, 5)
  assert swap_values(None, 10)==None
  assert swap_values(5, None)==None
  assert swap_values(7, 7)==(7, 7)
  assert swap_values(None, None)==None
output: def swap_values(a, b):
      if a is None or b is None:
          return None
      return (b, a)