input: Write a python function to invert a dictionary such that the keys become values and the values become keys.
  assert invert_dict({0:1, 1:2, 2:3, 3:4, 4:4}) == {1:0, 2:1, 3:2, 4:4}
  assert invert_dict({1: 'a', 2: 'b', 3: 'c'}) == {'a': 1, 'b': 2, 'c': 3}
  assert invert_dict({}) == {}
output: def invert_dict(d):
      return {v: k for k, v in d.items()}