Today, let's move on to the next topic in the Python Coding Challenge:

*Dictionaries & Sets*
*What is a Dictionary in Python?*

A dictionary is an unordered, mutable collection that stores data in key-value pairs.

*Example:*

student =
name: Amit,
age: 21,
course: Python


print(student[name]) Output: Amit

- Keys must be unique and immutable (like strings, numbers).
- Values can be anything: strings, numbers, lists, or even other dictionaries.


*Common Dictionary Methods:*

student.get(age) Returns 21
student.keys() Returns all keys
student.values() Returns all values
student.items() Returns key-value pairs
student[grade] = A+ Adds a new key-value pair

*What is a Set in Python?*

A set is an unordered collection of unique elements.

*Example* :

numbers = 1, 2, 3, 4, 4, 2
print(numbers) Output: 1, 2, 3, 4 — no duplicates

- Sets remove duplicates automatically.
- Useful for membership checks, uniqueness, and set operations (union, intersection).


✅ *Real-Life Project: Contact Book using Dictionary*

- Build a CLI-based contact book where users can:
- Add new contacts (name, phone)
- View all contacts
- Search by name
- Delete a contact


*Python Code:*

contacts =

while True:
print(n1. Add Contactn2. View Alln3. Searchn4. Deleten5. Exit)
choice = input(Enter choice: )

if choice == '1':
name = input(Name: )
phone = input(Phone: )
contacts[name] = phone
print(Contact saved!)

elif choice == '2':
for name, phone in contacts.items():
print(fname : phone)

elif choice == '3':
name = input(Enter name to search: )
if name in contacts:
print(fname's phone: contacts[name])
else:
print(Contact not found.)

elif choice == '4':
name = input(Enter name to delete: )
if name in contacts:
del contacts[name]
print(Deleted successfully.)
else:
print(No such contact.)

elif choice == '5':
break
else:
print(Invalid choice.)