choose_N.py

import random
 
def choose_N(matrix):
    """Choose N elements from an N x N square matrix, such that;
        1. The elements are chosen at-random
        2. One element per row
        3. One element per column
    """
    assert isinstance(matrix, list)
    columns =  range( len(matrix) )
    rows =  range ( len(matrix) )
 
    random.shuffle(columns)
    random.shuffle(rows)
 
    chosen = []
 
    for i in range( len(matrix) ):
        # Make sure we have a square matrix
        assert isinstance(matrix[i], list)
        assert len(matrix[i]) == len(matrix)
 
        chosen.append(matrix[ columns[i] ][ rows[i] ])
 
    return chosen