The Collections

💡

All the notes. All the examples. All in one place. The challenges prove you understand it. Solve them all and you mastered The Collections.

▶📝 Cheatsheet

1. Lists

A variable holds one thing. A list holds many things. Your phone contacts, your playlist, your grocery list. One name, many items inside.

python

fruits = ["apple", "banana", "mango"]
print(fruits)

Accessing items

python

print(fruits[0])       # apple
print(fruits[-1])      # mango

Adding and removing

python

fruits.append("orange")
fruits.remove("banana")
print(fruits)          # ["apple", "mango", "orange"]

Length

python

print(len(fruits))     # 3

Looping through a list

python

for fruit in fruits:
    print(fruit)

Check if item exists

python

if "mango" in fruits:
    print("Yes!")

Sorting

python

numbers = [5, 2, 8, 1, 9]
numbers.sort()
print(numbers)         # [1, 2, 5, 8, 9]

2. Tuples & Sets

Tuples

List but can't be changed

python

grades = (88, 72, 95, 60, 84)
print(grades[0])       # 88

grades[0] = 90         # ERROR - can't change a tuple

When to use tuples

python

days = ("Mon", "Tue", "Wed", "Thu", "Fri")
months = ("Jan", "Feb", "Mar", "Apr", "May")

Sets

List with no duplicates

python

cities = {"Oslo", "London", "Oslo", "Nairobi", "London"}
print(cities)     # {"Oslo", "London", "Nairobi"}

Removing duplicates from a list

python

names = ["Ahmed", "Hodan", "Ahmed", "Nimo", "Hodan"]
unique = set(names)
print(unique)     # {"Ahmed", "Hodan", "Nimo"}

3. Dictionaries

A list uses numbers to find things. A dictionary uses names. You look up the key, you get the value.

python

student = {
    "name": "Ahmed",
    "age": 22,
    "city": "Oslo"
}
print(student["name"])     # Ahmed

Adding and updating

python

student["email"] = "ahmed@email.com"
student["age"] = 23

List of dictionaries

python

students = [
    {"name": "Ahmed", "score": 85},
    {"name": "Hodan", "score": 92},
    {"name": "Bile", "score": 67}
]

for s in students:
    print(f"{s['name']}: {s['score']}")

🧾 Reference Table

Concept	Syntax	Example
Create a list	[item, item]	fruits = ["apple", "banana"]
Access item	list[index]	fruits[0]
Last item	list[-1]	fruits[-1]
Add item	.append()	fruits.append("mango")
Remove item	.remove()	fruits.remove("apple")
Length	len()	len(fruits)
Check if exists	in	"apple" in fruits
Sort	.sort()	numbers.sort()
Create a tuple	(item, item)	grades = (88, 72, 95)
Create a set	{item, item}	cities = {"Oslo", "London"}
Remove duplicates	set()	set(names)
Create a dict	{"key": value}	{"name": "Ahmed"}
Access value	dict["key"]	student["name"]
Add/update	dict["key"] = value	student["age"] = 23
All values	.values()	student.values()

▶🧩 Challenges

Challenge 1: My Friends

Create a list of 4 friends. Print the first one and the last one.

plain text

First: Ahmed
Last: Nimo

Challenge 2: Add and Remove

Create a list: ["Rice", "Chicken", "Bread"]. Add "Milk" to the end. Remove "Chicken". Print the list.

plain text

['Rice', 'Bread', 'Milk']

Challenge 3: Highest Score

A list of 5 scores: [88, 72, 95, 60, 84]. Print the highest and lowest.

plain text

Highest: 95
Lowest: 60

Challenge 4: Remove Duplicates

Cities visited: ['Oslo', 'London', 'Oslo', 'Nairobi', 'London']. Put them in a set and print the unique cities.

plain text

Unique: {'Oslo', 'London', 'Nairobi'}

Challenge 5: Student Card

Create a dictionary for a student: name, age, city. Print each value.

plain text

Name: Ahmed
Age: 22
City: Oslo

Challenge 6: Update Profile

Same student dictionary. Update the city to "London". Add an email. Print all values.

plain text

Name: Ahmed
Age: 22
City: London
Email: ahmed@email.com

Challenge 7: Phone Book

Create a dictionary with 3 contacts (name: phone). Ask the user for a name. If found, print the number. If not, print "Not found."

plain text

Search: Ahmed
Ahmed: 98765432

Challenge 8: Shopping List

Ask the user to add items one by one. Type "done" to stop. Print the final list and total items.

plain text

Add item: Milk
Add item: Bread
Add item: Eggs
Add item: done

1. Milk
2. Bread
3. Eggs
Total: 3

Challenge 9: Class Results

Given this list of students:

python

students = [
    {"name": "Ahmed", "score": 85},
    {"name": "Bile", "score": 45},
    {"name": "Nimo", "score": 67}
]

Pass is 60. Print pass or fail for each.

plain text

Ahmed: 85 - Pass
Bile: 45 - Fail
Nimo: 67 - Pass

Challenge 10: Product Lookup

Given this list of products:

python

products = [
    {"name": "Laptop", "price": 999},
    {"name": "Phone", "price": 699},
    {"name": "Headphones", "price": 149}
]

Ask the user for a product. If found, print the price. If not, print "Not found."

plain text

Search: Laptop
Laptop: $999

plain text

Search: Tablet
Not found.

Concept

Syntax

Example

Create a list

[item, item]

fruits = ["apple", "banana"]

Access item

list[index]

fruits[0]

Last item

list[-1]

fruits[-1]

Add item

.append()

fruits.append("mango")

Remove item

.remove()

fruits.remove("apple")

Length

len()

len(fruits)

Check if exists

"apple" in fruits

Sort

.sort()

numbers.sort()

Create a tuple

(item, item)

grades = (88, 72, 95)

Create a set

{item, item}

cities = {"Oslo", "London"}

Remove duplicates

set()

set(names)

Create a dict

{"key": value}

{"name": "Ahmed"}

Access value

dict["key"]

student["name"]

Add/update

dict["key"] = value

student["age"] = 23

All values

.values()

student.values()