input: Write a function to generate a Python script that contains a function with two parameters and returns the sum of the two parameters.
  def add(x, y):
      """Returns the sum of x and y"""
      return x + y
  
  assert add(3, 4)==7
  assert add(0, 0)==0
  assert add(-1, 1)==0
  assert add(5, -3)==2
  assert add(-2, -2)==-4
output: def add(x, y):
      return x + y