claire_et_guillaume.py

import argparse


if __name__ == '__main__':

    parser = argparse.ArgumentParser()
    parser.add_argument('-s', help='input string, dir arrows if none')
    parser.add_argument('-n', type=int, default=10)
    args = parser.parse_args()

    N = args.n
    # 2d array of size N
    a = [[['.'] for _ in range(N)] for _ in range(N)]
    # transpose of a; note that updating a will update b (and vice
    # versa) since the inner cells are references (i.e. lists of size 1)
    b = [[a[i][j] for i in range(N)] for j in range(N)]

    i, j, k = 0, 0, 0

    for m in range(N):

        for c, _i, j0, j1, j2, _s in [
                (a, m, m, N - m - 1, 1, '>'), (b, N - m - 1, m, N - m - 1, 1, 'v'),
                (a, N - m - 1, N - m - 1, m, -1, '<'), (b, m, N - m - 1, m, -1, '^')
        ]:
            i = _i
            for j in range(j0, j1, j2):
                if args.s:
                    c[i][j][0] = args.s[k]
                    k = (k + 1) % len(args.s)
                else:
                    c[i][j][0] = _s

    print('\n'.join([''.join(s[0] for s in r) for r in a]))