script_7.py - Nested Lists (Matrix Operations)

Code

See script_7.py for full code.

Explanation

Line 10-14: 2D list (matrix) - List containing lists (nested structure) - board is list type - Each element is also a list (containing strings) - Represents 3x3 grid

Line 17: for row in board: - Iterates over outer list - row is a list (one row of the matrix)

Line 18: print(" | ".join(row)) - .join() is string method - Takes iterable of strings, joins with separator - " | " is the separator - Converts list ["X", "O", "-"] to string "X | O | -"

Line 22: if board[row][col] == "-": - Double indexing for 2D access - board[row] gets the row list - [col] gets element from that row - Equivalent to: the_row = board[row]; value = the_row[col]

Line 23: board[row][col] = player - Assignment to nested index - Modifies element in the 2D structure - Changes value at specific coordinates

Line 49: diagonal = [matrix[i][i] for i in range(len(matrix))] - List comprehension accessing diagonal - i is both row and column index - Gets matrix[0][], matrix[1][], matrix[2][]

Line 53: transposed = [[matrix[j][i] for j in range(len(matrix))] for i in range(len(matrix[0]))] - Nested list comprehension - Outer comprehension creates rows - Inner comprehension creates columns - Swaps rows and columns (transpose operation)