Phone Book

Write a program called Phone Book that lets the user keep track of phone numbers. The program should use a dictionary to store phone numbers, and should allow the user to add numbers to the phone book and also lookup numbers in the phone book. Here's a sample run of the program:

Welcome to Phone Book!  This program stores phone numbers
of contacts.  You can add a new number, get a number,
or quit ('add', 'lookup', 'quit').
Enter your command at the prompt.
('add', 'lookup', 'quit') > lookup
name? Nick
Nick not found.
('add', 'lookup', 'quit') > add
name? Nick
number? > 666-555-4433
('add', 'lookup', 'quit') > lookup
name? Nick
666-555-4433
('add', 'lookup', 'quit') > quit

Your program should be able to handle 3 commands: 'quit', 'lookup' and 'add'. Quit should end the program. Lookup should prompt the user for a name and then print out the number stored for that name. If that name is not in the phone book, print an appropriate message. Add should prompt the user for a name and number, and then should add them to the phone book. If there was a previous entry with this same name, it should be overwritten.

We recommend implementing one command at a time, in this order:

1. quit
2. add
3. lookup

Hints

To create an empty dictionary, use:

my_dict = {}

To add an entry to a dictionary:

my_dict[key] = value

To get a value for a key in the dictionary:

my_dict[key]

To check if something is in the dictionary:

if key in my_dict:
    ...

To loop over all elements in a dictionary:

for key in my_dict:
    # do something with key and my_dict[key]
    ...