# This code demonstrates:
# (1) iterating through a dictionary to find all the keys associated with 
# a value.
# (2) the more general case: building an "inverted" dictionary.

def main():    
    # The owner of various phone numbers.
    phone = {'555-7632': 'Paul', '555-9832': 'Andrew',\
             '555-6677': 'Jen', '555-9823': 'Michael',\
             '555-6342' : 'Wael', '555-7343' : 'Paul',\
             '555-2222' : 'Michael'}
    
    # (1) Make a list of Paul's phone numbers.
    
    # Make a list of all the keys
    # If the key's value is Paul, take that key out 
    # Append all these keys together.
    
    pauls_phone_numbers = []
    for key in phone:
        if phone[key] == "Paul":
            # append that key to the list
            pauls_phone_numbers.append(key)
            
    print(pauls_phone_numbers)
    
    # (2) Make a new dictionary that is "inverted".
    # It will have names as keys, and the value for a name will be
    # the list of that person's phone numbers.
    inverted_dictionary = {}
    
    for (number, name) in phone.items():
        # In the inverted dictionary, we want to use name
        # as the key
        if name in inverted_dictionary:
            # The name is already in the inverted dictionary.
            # So it already has a value (a list of numbers).
            # Append to that.
            inverted_dictionary[name].append(number)
        else:
            # Name is not in the inverted dictionary yet.  Add it, with its
            # number.
            inverted_dictionary[name] = [number]
            
    print(inverted_dictionary)

main()