input: Write a Python function to swap the keys and values in a dictionary.
  assert swap_dict({"a": 1, "b": 2, "c": 3}) == {1: "a", 2: "b", 3: "c"}
  assert swap_dict({"apple": "fruit", "carrot": "vegetable"}) == {"fruit": "apple", "vegetable": "carrot"}
  assert swap_dict({1: "one", 2: "two", 3: "three"}) == {"one": 1, "two": 2, "three": 3}
output: def swap_dict(d):
      return {v: k for k, v in d.items()}