📚 Topic 07 · Collections
Data Structures
Master Python's built-in collections — lists, dictionaries, tuples, and sets — and learn when to use each one.
⏱ ~50 min
🟡 Intermediate
🗂️ Core
Lists
Ordered, mutable sequences. The most versatile collection in Python.
lists.py
fruits = ["apple", "banana", "cherry"]
fruits.append("date") # add to end
fruits.insert(1, "avocado") # insert at index
fruits.remove("banana") # remove by value
popped = fruits.pop() # remove and return last
print(fruits[0]) # apple
print(fruits[-1]) # last element
print(fruits[1:3]) # slice
# List comprehension
squares = [x**2 for x in range(5)]
print(squares) # [0, 1, 4, 9, 16]
Dictionaries
Key-value stores with O(1) lookup. Keys must be unique and immutable.
dicts.py
person = {"name": "Alice", "age": 30}
print(person["name"]) # Alice
print(person.get("height", "N/A")) # N/A (safe)
person["email"] = "alice@mail.com" # add/update
del person["age"] # delete key
for key, value in person.items():
print(f"{key} → {value}")
Tuples
Immutable ordered sequences. Use when data must not change — coordinates, RGB values, database records.
tuples.py
point = (10, 20)
x, y = point # unpacking
print(x, y) # 10 20
# Tuples can be used as dict keys (lists cannot)
grid = {(0, 0): "origin"}
Sets
Unordered collections of unique items. Perfect for membership tests and deduplication.
sets.py
tags = {"python", "coding", "python"}
print(tags) # {'coding', 'python'} — no duplicates
a = {1, 2, 3}
b = {2, 3, 4}
print(a | b) # union: {1,2,3,4}
print(a & b) # intersection: {2,3}
print(a - b) # difference: {1}
print("python" in tags) # True — O(1) lookup 📌 Which collection to choose? Need order + duplicates → list. Need key-value pairs → dict. Need immutable sequence → tuple. Need uniqueness + fast lookup → set.
