input: Write a function to swap the values of two variables in Python. If two variables are given as inputs, the function should return the swapped values of these two variables. If no variables are given, the function should return a message indicating no variables to swap.
  assert swap_values(5, 10)==(10, 5)
  assert swap_values(0, 0)==(0, 0)
  assert swap_values("a", "b")==("b", "a")
  assert swap_values(True, False)==(False, True)
  assert swap_values()== "No variables to swap"
output: def swap_values(a=None, b=None):
      if a is None and b is None:
          return "No variables to swap"
      return b, a