Contact Book

📇 Contact Book

🎮 What We're Building

A contact book storing name, phone, and email per contact, supporting adding new contacts, searching/listing them, editing an existing contact's details, and deleting one — all persisted to a JSON file between runs.

Step 1: Representing a Contact

Copycontact = {"name": "Ada Lovelace", "phone": "555-0100", "email": "ada@example.com"}

Same "plain dict, no class" approach as Chapter 4's tasks — a contact is just three related pieces of string data (Course 1, Chapters 5 and 7).

Step 2: Create — Adding a Contact

Copydef add_contact(contacts, name, phone, email):
    contacts.append({"name": name, "phone": phone, "email": email})

Step 3: Read — Listing and Searching

Copydef list_contacts(contacts):
    for i, c in enumerate(contacts, start=1):
        print(f"{i}. {c['name']} — {c['phone']} — {c['email']}")

def search_contacts(contacts, query):
    query = query.lower()
    return [c for c in contacts if query in c["name"].lower()]

search_contacts reuses a list comprehension (Course 1/2) with a substring in check — .lower() on both sides makes the search case-insensitive, so searching "ada" still finds "Ada Lovelace".

Step 4: Update — Editing a Contact

Copydef update_contact(contacts, index, field, new_value):
    if 0 <= index < len(contacts):
        contacts[index][field] = new_value
    else:
        print("Invalid contact number.")

The same bounds-checked guard clause from Chapter 4's complete_task. contacts[index][field] = new_value reassigns one key on the target contact's dict directly — field can be "name", "phone", or "email", letting one function handle updating any of the three.

Step 5: Delete — Removing a Contact

Copydef delete_contact(contacts, index):
    if 0 <= index < len(contacts):
        del contacts[index]
    else:
        print("Invalid contact number.")

del contacts[index] reuses del from Course 1, Chapter 7's dictionary coverage — it works on list items too, removing exactly the one element at that position and shifting the rest down.

Step 6: Tying It Together — Load, Save, and the Menu Loop

Copyimport json
from pathlib import Path

FILE = Path("contacts.json")

def load_contacts():
    if not FILE.exists():
        return []
    return json.loads(FILE.read_text())

def save_contacts(contacts):
    FILE.write_text(json.dumps(contacts, indent=2))

Identical load/save shape to Chapter 4's to-do app — this pattern (a Path, a load_ function returning [] if the file doesn't exist yet, a save_ function writing the whole list back) is worth recognizing as reusable across almost any small JSON-backed CLI tool, not something unique to contacts or tasks specifically.

🏁 The Complete Contact Book

Copyimport json
from pathlib import Path

FILE = Path("contacts.json")

def load_contacts():
    if not FILE.exists():
        return []
    return json.loads(FILE.read_text())

def save_contacts(contacts):
    FILE.write_text(json.dumps(contacts, indent=2))

def add_contact(contacts, name, phone, email):
    contacts.append({"name": name, "phone": phone, "email": email})

def list_contacts(contacts):
    for i, c in enumerate(contacts, start=1):
        print(f"{i}. {c['name']} — {c['phone']} — {c['email']}")

def search_contacts(contacts, query):
    query = query.lower()
    return [c for c in contacts if query in c["name"].lower()]

def update_contact(contacts, index, field, new_value):
    if 0 <= index < len(contacts):
        contacts[index][field] = new_value
    else:
        print("Invalid contact number.")

def delete_contact(contacts, index):
    if 0 <= index < len(contacts):
        del contacts[index]
    else:
        print("Invalid contact number.")

contacts = load_contacts()

while True:
    print("\n1. Add  2. List  3. Search  4. Update  5. Delete  6. Quit")
    choice = input("Choose an option: ")

    if choice == "1":
        name = input("Name: ")
        phone = input("Phone: ")
        email = input("Email: ")
        add_contact(contacts, name, phone, email)
        save_contacts(contacts)
    elif choice == "2":
        list_contacts(contacts)
    elif choice == "3":
        query = input("Search for: ")
        for c in search_contacts(contacts, query):
            print(f"{c['name']} — {c['phone']} — {c['email']}")
    elif choice == "4":
        list_contacts(contacts)
        num = int(input("Contact number to update: "))
        field = input("Field to update (name/phone/email): ")
        new_value = input("New value: ")
        update_contact(contacts, num - 1, field, new_value)
        save_contacts(contacts)
    elif choice == "5":
        list_contacts(contacts)
        num = int(input("Contact number to delete: "))
        delete_contact(contacts, num - 1)
        save_contacts(contacts)
    elif choice == "6":
        print("Goodbye!")
        break
    else:
        print("Not a valid option, try again.")

Note that options 4 and 5 both call list_contacts(contacts) first, before asking for a number — directly applying this chapter's own warn-box advice, so the number the user types always matches what they're currently looking at.

🎯 What's Next

Next chapter: Simple Web Scraper — introducing an external library, requests and BeautifulSoup.