6.20 Write function reverse() that takes as input a phone book, that is, a dictionary mapping names (the keys) to phone numbers (the values). The function should return another dictionary representing the reverse phone book mapping phone numbers (the keys) to the names (the values). >>> phonebook ['smith, Jane: 123-45-67', Doe, John': 987-65-43','Baker,David: 567-89-01) >>>reverse(phonebook) [123-45-67: Smith, Jane', "567-89-01: Baker,David', "987-65-43': 'Doe, John')