DEV Community

Ameh Mathias Ejeh
Ameh Mathias Ejeh

Posted on

Contact Book App

Project Overview

This is a console-based application that allows users to manage a basic contact list. It leverages Python's dictionary data structure to store contact names and their corresponding phone numbers. The application provides a menu-driven interface for adding new contacts, looking up existing ones, listing all stored contacts, and deleting contacts.

Features

  • Add Contact: Allows users to input a contact's name and phone number, which are then stored in the contact book.
  • Look Up Contact: Users can search for a contact by name, and if found, the application displays their phone number. It handles cases where the contact does not exist.
  • List All Contacts: Displays all stored contact names and their phone numbers in an easy-to-read format. It also informs the user if the contact book is empty.
  • Delete Contact: Provides the ability to remove an existing contact from the book by name. It includes checks for an empty book and for contacts not found.
  • Menu-Driven Interface: Guides the user through options with clear prompts.
  • Continuous Operation: Runs in a loop, allowing multiple operations until the user chooses to exit.

How to Use

Prerequisites

  • Python 3.x installed on your system.

Running the Application

  • Save the code: Save the provided Python code into a file named contact_book.py (or any other .py extension).
  • Open a terminal/command prompt: Navigate to the directory where you saved contact_book.py.
  • Run the script: Execute the command: 
python contact_book.py
Enter fullscreen mode Exit fullscreen mode

Interacting with the App

Upon running, you will see the main menu:

--- Simple Contact Book Menu ---
1. Add a new contact
2. Look up a contact
3. List all contacts
4. Delete a contact
5. Exit
Enter your choice (1-5):
Enter fullscreen mode Exit fullscreen mode
  • To Add a New Contact (Option 1):
    • Enter 1and press Enter.
    • Follow the prompts to enter the contact's name and phone number.
    • A confirmation message will be displayed.
  • To Look Up a Contact (Option 2):
    • Enter 2and press Enter.
    • Enter the name of the contact you wish to find.
    • The app will display the contact's phone number or indicate if the contact is not found.
  • To List All Contacts (Option 3):
    • Enter 3and press Enter.
    • The app will display all contacts stored in the book, or a message if the book is empty.
  • To Delete a Contact (Option 4):
    • Enter 4and press Enter.
    • The app will first list current contacts for reference.
    • Enter the name of the contact you wish to delete.
    • A confirmation message will be displayed if successful, or a "not found" message if the contact doesn't exist.
  • To Exit the App (Option 5):
    • Enter 5and press Enter.
    • The app will print a goodbye message and terminate.
  • Invalid Choice: If you enter any number or text that is not a valid menu option, the app will prompt you to try again.

Code Structure

The application's logic is contained within a single Python script (contact_book.py) and is structured as follows:

  • contacts = {}: An empty Python dictionary initialized at the beginning. This dictionaryis the core data structure, storing name: phone_number pairs.
  • while True: loop: The primary loop that keeps the application running, continuously presenting the menu and processing user input until an explicit exit command.
  • Menu Display: print() statements inside the loop present the user with the available options.
  • User Input: input() captures the user's menu choice.
  • Conditional Logic (if/elif/else):
    • if choice == '1': Handles adding a contact. It takes nameand phone_number input and adds them to the contactsdictionary using contacts[name] = phone_number.
    • elif choice == '2': Handles looking up a contact. It takes a nameas input and uses the inoperator (if name in contacts:) to check for the key's existence before attempting to retrieve and print its value (contacts[name]).
    • elif choice == '3': Handles listing all contacts. It checks if the contactsdictionary is empty (len(contacts) == 0 or if not contacts:). If not empty, it iterates through all key-value pairs using for name, number in contacts.items(): and prints them.
    • elif choice == '4': Handles deleting a contact. It first checks if the dictionary is empty. If not, it prompts for a name to delete, checks if the name exists using in, and then uses del contacts[name_to_delete] to remove the entry. Provides feedback for success or if the contact is not found.
    • elif choice == '5': Handles exiting the app. It prints a goodbye message and uses breakto terminate the whileloop.
    • else: Catches invalid menu choices.

Key Concepts Demonstrated

This project effectively utilizes and reinforces the following fundamental Python programming concepts:

  • Data Structures: Extensive use of Dictionaries (dict) for storing and managing key-value pairs (contacts).
    • Dictionary methods like .items().
    • Dictionary operations like adding/updating (dict[key] = value), accessing (dict[key]), and deleting (del dict[key]).
    • Checking for key existence using the inoperator.
  • Variables: Storing names, phone numbers, user choices, and the contacts dictionary.
  • Input/Output: Using input() for user interaction and print() for displaying information.
  • Logic & Control Flow:
    • whileLoop: For the continuous operation of the application.
    • if/elif/else Statements: For decision-making based on user menu choices and dictionary conditions.
    • forLoop: For iterating through dictionary items to display all contacts.
    • breakKeyword: For gracefully exiting the main application loop.
  • String Formatting: Using f-strings (f"...") for clear and dynamic output messages.

Top comments (0)