input: Write a function to swap the values of two variables. The function should take two arguments, swap their values, and return the new values of both variables.
  assert swap_variables(5, 10)==(10, 5)
  assert swap_variables(100, 3)==(3, 100)
  assert swap_variables(0, 0)==(0, 0)
  assert swap_variables(-1, 1)==(1, -1)
output: def swap_variables(a, b):
      return b, a