Python Nested Lists

List Satellite

Nested Lists

Represent grids, matrices, and hierarchies by embedding lists. Learn how to access, copy, and iterate them safely.

Access elementsCopy correctly

Creation

grid = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9],
]

Avoid [[0] * 3] * 4 because it reuses references. Prefer comprehensions:

grid = [[0 for _ in range(cols)] for _ in range(rows)]

Access

grid[row][col]

Loop over rows and columns:

for r, row in enumerate(grid):
    for c, value in enumerate(row):
        ...

Next up in your learning path

Copy lists

Use deepcopy for nested structures.

Companion

List slicing

Slice rows/columns cleanly.

Technique

List comprehensions

Build nested lists with nested comprehensions.

Practice