Of course! Here is a comprehensive guide to creating a Python Address Book, starting with a simple version and building up to a more feature-rich, file-based application.

Part 1: A Simple In-Memory Address Book

This version stores contacts in a Python dictionary. It's a great starting point to understand the core logic.

The Code

# A simple in-memory address book
def add_contact(address_book):
    """Adds a new contact to the address book."""
    print("\n--- Add a New Contact ---")
    name = input("Enter name: ")
    phone = input("Enter phone number: ")
    email = input("Enter email address: ")
    # Store the contact details in a dictionary
    contact = {
        "name": name,
        "phone": phone,
        "email": email
    }
    # Use the name as the key for easy lookup
    address_book[name] = contact
    print(f"Contact '{name}' added successfully!")
def view_all_contacts(address_book):
    """Displays all contacts in the address book."""
    print("\n--- All Contacts ---")
    if not address_book:
        print("No contacts found.")
        return
    for name, details in address_book.items():
        print(f"Name: {name}")
        print(f"  Phone: {details['phone']}")
        print(f"  Email: {details['email']}")
        print("-" * 20)
def search_contact(address_book):
    """Searches for a contact by name."""
    print("\n--- Search for a Contact ---")
    search_term = input("Enter the name to search for: ")
    found = False
    for name, details in address_book.items():
        # Case-insensitive search
        if search_term.lower() in name.lower():
            print("\n--- Contact Found ---")
            print(f"Name: {name}")
            print(f"  Phone: {details['phone']}")
            print(f"  Email: {details['email']}")
            found = True
    if not found:
        print(f"No contact found with the name '{search_term}'.")
def delete_contact(address_book):
    """Deletes a contact by name."""
    print("\n--- Delete a Contact ---")
    name_to_delete = input("Enter the name of the contact to delete: ")
    if name_to_delete in address_book:
        del address_book[name_to_delete]
        print(f"Contact '{name_to_delete}' deleted successfully.")
    else:
        print(f"Contact '{name_to_delete}' not found.")
def main():
    """Main function to run the address book application."""
    address_book = {}  # The address book is a dictionary
    while True:
        print("\n===== Address Book Menu =====")
        print("1. Add Contact")
        print("2. View All Contacts")
        print("3. Search Contact")
        print("4. Delete Contact")
        print("5. Exit")
        choice = input("Enter your choice (1-5): ")
        if choice == '1':
            add_contact(address_book)
        elif choice == '2':
            view_all_contacts(address_book)
        elif choice == '3':
            search_contact(address_book)
        elif choice == '4':
            delete_contact(address_book)
        elif choice == '5':
            print("Exiting Address Book. Goodbye!")
            break
        else:
            print("Invalid choice. Please enter a number between 1 and 5.")
# Run the main function when the script is executed
if __name__ == "__main__":
    main()

How to Run It

1. Save the code as a Python file (e.g., simple_address_book.py).
2. Run it from your terminal: python simple_address_book.py
3. Follow the on-screen menu.

Limitation

The biggest problem with this version is that all data is lost when you close the program. The address_book dictionary exists only in the computer's memory.

Part 2: A File-Based Address Book (Persistent Storage)

This version improves upon the first by saving contacts to a file. This way, your address book will remember the contacts between sessions. We'll use Python's built-in json module, which is perfect for storing structured data like dictionaries.

The Code

import json
import os
# File to store the address book
ADDRESS_BOOK_FILE = "address_book.json"
def load_address_book():
    """Loads the address book from a JSON file."""
    if os.path.exists(ADDRESS_BOOK_FILE):
        try:
            with open(ADDRESS_BOOK_FILE, 'r') as f:
                return json.load(f)
        except (json.JSONDecodeError, FileNotFoundError):
            # If the file is empty or corrupted, start fresh
            return {}
    else:
        # If the file doesn't exist, create a new one
        return {}
def save_address_book(address_book):
    """Saves the address book to a JSON file."""
    with open(ADDRESS_BOOK_FILE, 'w') as f:
        json.dump(address_book, f, indent=4) # indent=4 makes the file readable
# --- Functions from Part 1 are mostly the same ---
def add_contact(address_book):
    """Adds a new contact to the address book and saves it."""
    print("\n--- Add a New Contact ---")
    name = input("Enter name: ")
    phone = input("Enter phone number: ")
    email = input("Enter email address: ")
    if name in address_book:
        print(f"Contact '{name}' already exists. Use 'Update Contact' instead.")
        return
    contact = {"name": name, "phone": phone, "email": email}
    address_book[name] = contact
    save_address_book(address_book)
    print(f"Contact '{name}' added successfully!")
def view_all_contacts(address_book):
    """Displays all contacts in the address book."""
    print("\n--- All Contacts ---")
    if not address_book:
        print("No contacts found.")
        return
    for name, details in address_book.items():
        print(f"Name: {details['name']}") # Use details['name'] for consistency
        print(f"  Phone: {details['phone']}")
        print(f"  Email: {details['email']}")
        print("-" * 20)
def search_contact(address_book):
    """Searches for a contact by name."""
    print("\n--- Search for a Contact ---")
    search_term = input("Enter the name to search for: ")
    found = False
    for name, details in address_book.items():
        if search_term.lower() in name.lower():
            print("\n--- Contact Found ---")
            print(f"Name: {details['name']}")
            print(f"  Phone: {details['phone']}")
            print(f"  Email: {details['email']}")
            found = True
    if not found:
        print(f"No contact found with the name '{search_term}'.")
def delete_contact(address_book):
    """Deletes a contact by name and saves the change."""
    print("\n--- Delete a Contact ---")
    name_to_delete = input("Enter the name of the contact to delete: ")
    if name_to_delete in address_book:
        del address_book[name_to_delete]
        save_address_book(address_book)
        print(f"Contact '{name_to_delete}' deleted successfully.")
    else:
        print(f"Contact '{name_to_delete}' not found.")
def update_contact(address_book):
    """Updates an existing contact's details."""
    print("\n--- Update a Contact ---")
    name_to_update = input("Enter the name of the contact to update: ")
    if name_to_update in address_book:
        contact = address_book[name_to_update]
        print(f"Current details for {name_to_update}:")
        print(f"  Phone: {contact['phone']}")
        print(f"  Email: {contact['email']}")
        print("\nEnter new details (leave blank to keep current):")
        new_phone = input(f"New phone [{contact['phone']}]: ") or contact['phone']
        new_email = input(f"New email [{contact['email']}]: ") or contact['email']
        contact['phone'] = new_phone
        contact['email'] = new_email
        save_address_book(address_book)
        print(f"Contact '{name_to_update}' updated successfully.")
    else:
        print(f"Contact '{name_to_update}' not found.")
def main():
    """Main function to run the address book application."""
    address_book = load_address_book()
    while True:
        print("\n===== Address Book Menu =====")
        print("1. Add Contact")
        print("2. View All Contacts")
        print("3. Search Contact")
        print("4. Update Contact") # New option
        print("5. Delete Contact")
        print("6. Exit")
        choice = input("Enter your choice (1-6): ")
        if choice == '1':
            add_contact(address_book)
        elif choice == '2':
            view_all_contacts(address_book)
        elif choice == '3':
            search_contact(address_book)
        elif choice == '4':
            update_contact(address_book)
        elif choice == '5':
            delete_contact(address_book)
        elif choice == '6':
            print("Exiting Address Book. Goodbye!")
            break
        else:
            print("Invalid choice. Please enter a number between 1 and 6.")
if __name__ == "__main__":
    main()

Key Improvements in Version 2

1. File Handling (json module):
   • load_address_book(): Reads the address_book.json file when the program starts. If the file doesn't exist, it gracefully creates an empty dictionary.
   • save_address_book(): Writes the current state of the address_book dictionary to the file. json.dump(address_book, f, indent=4) makes the saved file human-readable.
2. Persistent Data: Now, every time you add, update, or delete a contact, the save_address_book() function is called, saving your changes to the file.
3. Update Function: Added a new update_contact() function, which is a common and useful feature.
4. Consistent Display: The view_all_contacts now prints details['name'] to ensure consistency if you ever change the key.

How to Run It

1. Save the code as address_book.py.
2. Run it: python address_book.py.
3. After adding a few contacts and exiting, you will see a new file named address_book.json in the same directory. You can open it with any text editor to see your data stored in JSON format.

Part 3: Object-Oriented Approach (More Advanced)

For larger applications, organizing code into classes is a best practice. This version encapsulates the address book's logic and data within a class.

The Code

import json
import os
class Contact:
    """Represents a single contact."""
    def __init__(self, name, phone, email):
        self.name = name
        self.phone = phone
        self.email = email
    def to_dict(self):
        """Converts the contact object to a dictionary for JSON serialization."""
        return {"name": self.name, "phone": self.phone, "email": self.email}
class AddressBook:
    """Manages a collection of contacts."""
    def __init__(self, filename="address_book.json"):
        self.filename = filename
        self.contacts = {} # Using a dictionary for fast lookups by name
        self.load()
    def load(self):
        """Loads contacts from the JSON file."""
        if os.path.exists(self.filename):
            try:
                with open(self.filename, 'r') as f:
                    data = json.load(f)
                    # Rebuild Contact objects from the dictionary data
                    for name, details in data.items():
                        self.contacts[name] = Contact(name, details['phone'], details['email'])
            except (json.JSONDecodeError, FileNotFoundError):
                self.contacts = {}
    def save(self):
        """Saves all contacts to the JSON file."""
        # Convert all Contact objects to dictionaries before saving
        data = {name: contact.to_dict() for name, contact in self.contacts.items()}
        with open(self.filename, 'w') as f:
            json.dump(data, f, indent=4)
    def add_contact(self, contact):
        """Adds a new contact if the name doesn't already exist."""
        if contact.name in self.contacts:
            print(f"Error: Contact '{contact.name}' already exists.")
            return False
        self.contacts[contact.name] = contact
        self.save()
        print(f"Contact '{contact.name}' added successfully.")
        return True
    def view_all_contacts(self):
        """Displays all contacts."""
        if not self.contacts:
            print("\nNo contacts found.")
            return
        print("\n--- All Contacts ---")
        for contact in self.contacts.values():
            print(f"Name: {contact.name}")
            print(f"  Phone: {contact.phone}")
            print(f"  Email: {contact.email}")
            print("-" * 20)
    def search_contact(self, search_term):
        """Searches for a contact by name."""
        found = False
        print(f"\n--- Search Results for '{search_term}' ---")
        for contact in self.contacts.values():
            if search_term.lower() in contact.name.lower():
                print(f"Name: {contact.name}")
                print(f"  Phone: {contact.phone}")
                print(f"  Email: {contact.email}")
                print("-" * 20)
                found = True
        if not found:
            print(f"No contacts found matching '{search_term}'.")
    def delete_contact(self, name):
        """Deletes a contact by name."""
        if name in self.contacts:
            del self.contacts[name]
            self.save()
            print(f"Contact '{name}' deleted successfully.")
            return True
        else:
            print(f"Error: Contact '{name}' not found.")
            return False
    def update_contact(self, name):
        """Updates an existing contact's details."""
        if name not in self.contacts:
            print(f"Error: Contact '{name}' not found.")
            return
        contact = self.contacts[name]
        print(f"\nUpdating details for {name}:")
        print(f"  Current Phone: {contact.phone}")
        print(f"  Current Email: {contact.email}")
        new_phone = input(f"Enter new phone (or leave blank to keep '{contact.phone}'): ") or contact.phone
        new_email = input(f"Enter new email (or leave blank to keep '{contact.email}'): ") or contact.email
        contact.phone = new_phone
        contact.email = new_email
        self.save()
        print(f"Contact '{name}' updated successfully.")
# --- Main Application Logic ---
def main():
    """Runs the command-line interface for the Address Book."""
    address_book = AddressBook()
    while True:
        print("\n===== Address Book Menu =====")
        print("1. Add Contact")
        print("2. View All Contacts")
        print("3. Search Contact")
        print("4. Update Contact")
        print("5. Delete Contact")
        print("6. Exit")
        choice = input("Enter your choice (1-6): ")
        if choice == '1':
            print("\n--- Add a New Contact ---")
            name = input("Enter name: ")
            phone = input("Enter phone number: ")
            email = input("Enter email address: ")
            new_contact = Contact(name, phone, email)
            address_book.add_contact(new_contact)
        elif choice == '2':
            address_book.view_all_contacts()
        elif choice == '3':
            search_term = input("Enter the name to search for: ")
            address_book.search_contact(search_term)
        elif choice == '4':
            name = input("Enter the name of the contact to update: ")
            address_book.update_contact(name)
        elif choice == '5':
            name = input("Enter the name of the contact to delete: ")
            address_book.delete_contact(name)
        elif choice == '6':
            print("Exiting Address Book. Goodbye!")
            break
        else:
            print("Invalid choice. Please enter a number between 1 and 6.")
if __name__ == "__main__":
    main()

Why Object-Oriented?

• Encapsulation: The AddressBook class manages its own data (self.contacts) and the logic to manipulate it (add, save, etc.). The main function doesn't need to know how it works, only what it can do.
• Organization: Code is split into logical classes (Contact, AddressBook), making it easier to read, maintain, and expand.
• Scalability: It's much easier to add new features to this structure (e.g., adding an address field to the Contact class) without cluttering the main application loop.