Contact Book with Search and Update 📞

Contact Book with Search and Update 📞 — A Step-by-Step Tutorial
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Creating a simple Contact Book app is a great exercise to understand core Python concepts like dictionaries, file handling, functions, and exception handling. In this tutorial, you’ll build an interactive command-line Contact Book that lets you add, update, delete, and search contacts, with all data saved persistently in a file.

What You’ll Learn
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How to use dictionaries to store contact information (name and phone number)
Persist data with file handling (load/save contacts)
Build a menu-driven program with loops and conditionals
Implement functions with exception handling for robust input
Format strings nicely for a user-friendly display

Step 1: Setup and Data Structure
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We’ll use a dictionary to store contacts:

contacts = {
    "Alice": "123-456-7890",
    "Bob": "987-654-3210"
}

Keys are names, values are phone numbers.

Step 2: Load and Save Contacts from File
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We’ll save contacts as JSON in contacts.json for easy persistence.

import json

def load_contacts(filename="contacts.json"):
    try:
        with open(filename, "r") as f:
            return json.load(f)
    except FileNotFoundError:
        return {}
    except json.JSONDecodeError:
        print("File corrupted! Starting with empty contact book.")
        return {}

def save_contacts(contacts, filename="contacts.json"):
    with open(filename, "w") as f:
        json.dump(contacts, f)

Step 3: Add a Contact
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Get user input for name and phone, validate, and save.

def add_contact(contacts):
    name = input("Enter contact name: ").strip().title()
    if not name:
        print("Name cannot be empty.")
        return
    if name in contacts:
        print("Contact already exists. Use update to change details.")
        return
    phone = input("Enter phone number: ").strip()
    if not phone:
        print("Phone number cannot be empty.")
        return
    contacts[name] = phone
    print(f"Contact {name} added.")

Step 4: Update a Contact
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Let user change existing contact’s phone.

def update_contact(contacts):
    name = input("Enter contact name to update: ").strip().title()
    if name not in contacts:
        print("Contact not found.")
        return
    phone = input(f"Enter new phone for {name}: ").strip()
    if not phone:
        print("Phone number cannot be empty.")
        return
    contacts[name] = phone
    print(f"Contact {name} updated.")

Step 5: Delete a Contact
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Remove a contact from the dictionary.

def delete_contact(contacts):
    name = input("Enter contact name to delete: ").strip().title()
    if name in contacts:
        del contacts[name]
        print(f"Contact {name} deleted.")
    else:
        print("Contact not found.")

Step 6: Search Contacts by Name or Phone
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Allow users to find contacts by part of the name or phone number.

def search_contacts(contacts):
    query = input("Enter name or phone to search: ").strip().lower()
    found = False
    for name, phone in contacts.items():
        if query in name.lower() or query in phone:
            print(f"{name}: {phone}")
            found = True
    if not found:
        print("No contacts matched your search.")

Step 7: Display All Contacts Nicely
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def list_contacts(contacts):
    if not contacts:
        print("No contacts saved.")
        return
    print("\nSaved Contacts:")
    print("-" * 20)
    for name, phone in sorted(contacts.items()):
        print(f"{name:<15} {phone}")
    print("-" * 20)

Step 8: Main Menu Loop
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Put everything together into a menu-driven app.

def main():
    contacts = load_contacts()

    while True:
        print("\n--- Contact Book Menu ---")
        print("1. Add Contact")
        print("2. Update Contact")
        print("3. Delete Contact")
        print("4. Search Contacts")
        print("5. List All Contacts")
        print("6. Save and Exit")

        choice = input("Choose an option (1-6): ")

        if choice == "1":
            add_contact(contacts)
        elif choice == "2":
            update_contact(contacts)
        elif choice == "3":
            delete_contact(contacts)
        elif choice == "4":
            search_contacts(contacts)
        elif choice == "5":
            list_contacts(contacts)
        elif choice == "6":
            save_contacts(contacts)
            print("Contacts saved. Goodbye! 👋")
            break
        else:
            print("Invalid choice. Please choose 1-6.")