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AIM

To write a program to input friends' names and their phone numbers, store them in a dictionary as key-value pairs, and perform various operations like display, add, delete, modify, search, and sort.

ALGORITHM

Start
Input the number of friends and create an empty dictionary
For each friend, input name and phone number and store in dictionary
Display the initial dictionary
Start a menu-driven loop with 7 options
Based on user choice, perform the following operations:
- Display all friends and their phone numbers
- Add a new friend to the dictionary
- Delete a friend using pop() method
- Modify phone number of an existing friend
- Search for a friend in the dictionary
- Display dictionary in sorted order of names
- Exit the program
Repeat until user chooses to exit
Stop

PROGRAM

# Friends Phone Directory Dictionary Operations

n = int(input("How many friends?"))
fd = {}

for i in range(n):
    print("Enter details of Friend:", (i+1))
    name = input("Name:")
    ph = int(input("Phone:"))
    fd[name] = ph

print("Friends dictionary is", fd)

ch = 0
while ch != 7:
    print("\t MENU")
    print("1. Display all Friends")
    print("2. Add a new Friend")
    print("3. Delete a Friend")
    print("4. Modify a Phone Number")
    print("5. Search for a Friend")
    print("6. Sort the Names")
    print("7. Exit")
    
    ch = int(input("Enter your choice(1 to 7):"))
    
    if ch == 1:
        print(fd)
    elif ch == 2:
        print("Enter Details of New Friend:")
        name = input("Name")
        ph = int(input("Phone:"))
        fd[name] = ph
    elif ch == 3:
        nm = input("Friend Name to be deleted:")
        res = fd.pop(nm, -1)
        if res != -1:
            print(res, "Deleted")
        else:
            print("No Such friend")
    elif ch == 4:
        name = input("Friend Name:")
        ph = int(input("Changed Phone:"))
        fd[name] = ph
    elif ch == 5:
        name = input("Friend Name:")
        if name in fd:
            print(name, "Exists in the dictionary.")
        else:
            print(name, "does not exist in the dictionary..")
    elif ch == 6:
        lst = sorted(fd)
        print("{", end='')
        for a in lst:
            print(a, ":", fd[a], end='')
        print("}")
    elif ch == 7:
        print("Exited successfully..")
        break
    else:
        print("Valid choices are 1 to 7")

OUTPUT

How many friends?3

Enter details of Friend: 1

Name:Alice

Phone:9876543210

Enter details of Friend: 2

Name:Bob

Phone:8765432109

Enter details of Friend: 3

Name:Charlie

Phone:7654321098

Friends dictionary is {"Alice": 9876543210, "Bob": 8765432109, "Charlie": 7654321098}

1. Display all Friends

2. Add a new Friend

3. Delete a Friend

4. Modify a Phone Number

5. Search for a Friend

6. Sort the Names

7. Exit

Enter your choice(1 to 7):1

{"Alice": 9876543210, "Bob": 8765432109, "Charlie": 7654321098}

Enter your choice(1 to 7):2

Enter Details of New Friend:

NameDiana

Phone:6543210987

Enter your choice(1 to 7):6

{"Alice": 9876543210 "Bob": 8765432109 "Charlie": 7654321098 "Diana": 6543210987}

ALTERNATIVE METHODS

Method 2: Using Functions

def display_friends(directory):
    if directory:
        print("\nFriends Directory:")
        for name, phone in directory.items():
            print(f"{name}: {phone}")
    else:
        print("No friends in directory!")

def add_friend(directory):
    name = input("Enter friend's name: ")
    phone = input("Enter phone number: ")
    directory[name] = phone
    print(f"{name} added successfully!")

def delete_friend(directory):
    name = input("Enter friend's name to delete: ")
    if name in directory:
        del directory[name]
        print(f"{name} deleted successfully!")
    else:
        print(f"{name} not found in directory!")

def modify_phone(directory):
    name = input("Enter friend's name: ")
    if name in directory:
        new_phone = input("Enter new phone number: ")
        directory[name] = new_phone
        print(f"{name}'s phone number updated!")
    else:
        print(f"{name} not found in directory!")

def search_friend(directory):
    name = input("Enter friend's name to search: ")
    if name in directory:
        print(f"{name}: {directory[name]}")
    else:
        print(f"{name} not found in directory!")

def sort_friends(directory):
    if directory:
        sorted_names = sorted(directory.keys())
        print("\nSorted Directory:")
        for name in sorted_names:
            print(f"{name}: {directory[name]}")
    else:
        print("No friends to sort!")

def main():
    friends = {}
    
    # Initial input
    n = int(input("How many friends? "))
    for i in range(n):
        name = input(f"Enter name of friend {i+1}: ")
        phone = input(f"Enter phone number: ")
        friends[name] = phone
    
    while True:
        print("\n" + "="*30)
        print("FRIENDS DIRECTORY MENU")
        print("="*30)
        print("1. Display all friends")
        print("2. Add new friend")
        print("3. Delete friend")
        print("4. Modify phone number")
        print("5. Search friend")
        print("6. Sort friends")
        print("7. Exit")
        
        choice = input("Enter your choice (1-7): ")
        
        if choice == '1':
            display_friends(friends)
        elif choice == '2':
            add_friend(friends)
        elif choice == '3':
            delete_friend(friends)
        elif choice == '4':
            modify_phone(friends)
        elif choice == '5':
            search_friend(friends)
        elif choice == '6':
            sort_friends(friends)
        elif choice == '7':
            print("Thank you for using Friends Directory!")
            break
        else:
            print("Invalid choice! Please try again.")

if __name__ == "__main__":
    main()

Method 3: Using Dictionary Methods

# Enhanced version using dictionary methods

def create_directory():
    friends = {}
    n = int(input("How many friends? "))
    
    for i in range(n):
        print(f"\nEnter details for friend {i+1}:")
        name = input("Name: ").strip().title()
        
        while True:
            try:
                phone = input("Phone: ").strip()
                # Basic phone validation
                if len(phone) >= 10 and phone.isdigit():
                    friends[name] = phone
                    break
                else:
                    print("Please enter a valid 10-digit phone number!")
            except ValueError:
                print("Invalid input! Please try again.")
    
    return friends

def display_all(friends):
    if not friends:
        print("\nNo friends in directory!")
        return
    
    print("\n" + "="*40)
    print("FRIENDS DIRECTORY")
    print("="*40)
    for name, phone in friends.items():
        print(f"{name:<20} : {phone}")
    print("="*40)

def add_new_friend(friends):
    name = input("\nEnter friend's name: ").strip().title()
    
    if name in friends:
        print(f"{name} already exists! Use modify option to change phone number.")
        return
    
    phone = input("Enter phone number: ").strip()
    friends[name] = phone
    print(f"\n{name} added successfully!")

def remove_friend(friends):
    if not friends:
        print("\nNo friends to delete!")
        return
    
    name = input("\nEnter friend's name to delete: ").strip().title()
    removed_phone = friends.pop(name, None)
    
    if removed_phone:
        print(f"\n{name} (Phone: {removed_phone}) deleted successfully!")
    else:
        print(f"\n{name} not found in directory!")

def update_phone(friends):
    if not friends:
        print("\nNo friends to modify!")
        return
    
    name = input("\nEnter friend's name: ").strip().title()
    
    if name in friends:
        old_phone = friends[name]
        new_phone = input(f"Current phone: {old_phone}\nEnter new phone: ").strip()
        friends[name] = new_phone
        print(f"\n{name}'s phone updated from {old_phone} to {new_phone}")
    else:
        print(f"\n{name} not found in directory!")

def find_friend(friends):
    if not friends:
        print("\nNo friends to search!")
        return
    
    name = input("\nEnter friend's name to search: ").strip().title()
    phone = friends.get(name)
    
    if phone:
        print(f"\nFound: {name} - {phone}")
    else:
        print(f"\n{name} not found in directory!")

def show_sorted(friends):
    if not friends:
        print("\nNo friends to sort!")
        return
    
    print("\n" + "="*40)
    print("SORTED FRIENDS DIRECTORY")
    print("="*40)
    
    for name in sorted(friends.keys()):
        print(f"{name:<20} : {friends[name]}")
    print("="*40)

def main():
    print("FRIENDS PHONE DIRECTORY")
    print("="*30)
    
    friends = create_directory()
    
    menu_options = {
        '1': ("Display all friends", display_all),
        '2': ("Add new friend", add_new_friend),
        '3': ("Delete friend", remove_friend),
        '4': ("Modify phone number", update_phone),
        '5': ("Search friend", find_friend),
        '6': ("Show sorted directory", show_sorted),
        '7': ("Exit", None)
    }
    
    while True:
        print("\n" + "="*30)
        print("MENU OPTIONS")
        print("="*30)
        for key, (description, _) in menu_options.items():
            print(f"{key}. {description}")
        print("="*30)
        
        choice = input("Enter your choice (1-7): ").strip()
        
        if choice == '7':
            print("\nThank you for using Friends Directory!")
            print("Goodbye!")
            break
        elif choice in menu_options:
            _, function = menu_options[choice]
            if function:
                function(friends)
        else:
            print("\nInvalid choice! Please enter a number between 1-7.")

if __name__ == "__main__":
    main()

CONCLUSION

Thus, the given program was successfully executed and the output was verified as per the expected result.

VIVA QUESTIONS

What is the advantage of using a dictionary over a list for storing phone directory data?
Dictionaries provide O(1) average time complexity for search, insert, and delete operations using keys, while lists require O(n) time for searching. Dictionaries also provide meaningful key-value associations.
What does the pop() method return when the key is not found?
The pop() method returns the default value (second argument) if the key is not found. In our program, pop(nm, -1) returns -1 when the friend's name is not found, allowing us to handle the error gracefully.
How does the sorted() function work with dictionaries?
sorted(fd) returns a sorted list of dictionary keys. To access the corresponding values, we iterate through the sorted keys and use them to retrieve values from the original dictionary.
What happens if we try to modify a phone number for a non-existent friend?
The program will create a new key-value pair in the dictionary. To prevent this, we should check if the key exists using 'if name in fd:' before modification.
How can we handle duplicate phone numbers in this program?
We can check if the phone number already exists by iterating through dictionary values or maintaining a reverse dictionary. We could also use validation to prevent duplicate entries.
What are the limitations of storing phone numbers as integers?
Storing as integers removes leading zeros, doesn't support international formats with '+' or '-', and may cause overflow for very large numbers. Strings are better for phone number storage.
How would you implement case-insensitive name searching?
Convert both the search key and dictionary keys to lowercase using .lower() method, or store all names in a consistent case (title case) when adding them to the dictionary.
How can this program be extended to store additional information about friends?
Instead of storing phone numbers as values, we can store dictionaries or lists containing multiple pieces of information like email, address, birthday, etc. For example: friends[name] = {"phone": ph, "email": email}.

Next Program: List Element Swapping

Class 11 Practical Programs

Friends Phone Directory Dictionary Operations

AIM