"""
Recommended Python Style Guide:
https://peps.python.org/pep-0008/#introduction
"""

# Defining a 4x4 matrix
M = [[-2,  5,  3,  2],
     [9, -6,  5,  1],
     [3,  2,  7,  3],
     [-1,  8, -4,  8]]

# Matrix printing, nicely formatted
for row in M:
    for val in row:
        print(f"{val:4}", end="")  # Print each value with 4-character width for alignment
    print()  # Move to the next line after printing each row

# Find the main diagonal
n = len(M)  # Number of rows (or columns, since it's a square matrix)
main_diagonal = [M[i][i] for i in range(n)]  # Extract the main diagonal elements (M[i][i])
print(f"Main_diagonal = {main_diagonal}")