Nested Lists0%
Nested Lists
Beginner9 min read•Updated: 2026-09-03
Nested Lists
Nested lists are lists containing other lists as elements, perfect for representing 2D tables, grids, and matrices.
Key Concepts & Detailed Explanation
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Code Examples & Output
Python
# 3x3 Tic-Tac-Toe / Coordinate grid
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
# Accessing nested elements: matrix[row][column]
print("Row 0, Col 0:", matrix[0][0]) # 1
print("Center element:", matrix[1][1]) # 5
# Iterating over nested list
print("Grid rows:")
for row in matrix:
for val in row:
print(val, end=" ")
print()
Expected Output:
Output
Row 0, Col 0: 1
Center element: 5
Grid rows:
1 2 3
4 5 6
7 8 9
Best Practices & Common Pitfalls
Beware of shallow copying nested lists. Use 'copy.deepcopy()' if inner lists need to be independent.
Practice Quiz
1. How do you access the value 5 in 'm = [[1, 2], [4, 5]]'?
- A) m[1, 1]
- B) m[1][1]
- C) m(1)(1)
- D) m[5]
Answer: B
Explanation: Two sets of brackets are used: m[row][column].
2. Why does '[[0]3]3' cause bugs when modifying one inner element?
- A) SyntaxError
- B) All rows reference the exact same list in memory
- C) Python doesn't support multiplication
- D) It creates tuples
Answer: B
Explanation: Multiplying a list copies the reference, so changing one row affects all rows.
Practice Challenge
Create a 3x3 matrix representing exam marks for 3 students across 3 subjects, and compute the average mark for each student.
Next Lesson
Tuple Introduction
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Related Lessons
| Previous Lesson | Next Lesson |
|---|---|
| List Methods | Tuple Introduction |
Practice Quiz
Test your understanding of this lesson with 1 questions. Each question has one correct answer.