input: Write a python function to reverse the key-value pairs in a dictionary.
  assert reverse_dict({'a':1, 'b':2, 'c':3}) == {1:'a', 2:'b', 3:'c'}
  assert reverse_dict({1:'one', 2:'two', 3:'three'}) == {'one':1, 'two':2, 'three':3}
  assert reverse_dict({'x':24, 'y':25, 'z':26}) == {24:'x', 25:'y', 26:'z'}
output: def reverse_dict(d):
      return {v: k for k, v in d.items()}