Creating a Two Dimensional Array in Python

Suppose you want to create an array with 4 rows and 3 columns.

Method 1: Using List Comprehension

cols = 3
rows = 4

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

This code creates:

[[0, 0, 0], [0, 0, 0], [0, 0, 0], [0, 0, 0]]

Do not use the following code (common pitfall):

table = [[0] * cols] * rows

If you modify one element, all rows will be affected because they reference the same list:

table = [[0] * cols] * rows
table[1][1] = 1
print(table)
# Output: [[0, 1, 0], [0, 1, 0], [0, 1, 0], [0, 1, 0]]

import numpy as np
table = np.zeros((4, 3))
print(table)
# Output:
# [[0. 0. 0.]
#  [0. 0. 0.]
#  [0. 0. 0.]
#  [0. 0. 0.]]

For non-zero initialization, replace 0 with any value you need.
For jagged (non-rectangular) arrays, use a list of lists with different lengths.
NumPy arrays are recommended for numerical computations and large data due to better performance and more features.