This code generates random patterns with ' ', +, and -

random_nft.py

import random

symbols = ['-', '+', ' ', ' ', ' ', ' ']

def get_symbol(seed: int = 1):
#    random.seed(seed)
    r = int(random.random() * 1000)
    return symbols[r % len(symbols)]

matrix = [[get_symbol(i + j) for i in range(40)] for j in range(20)]

def print_matrix():
    output = ""
    for i in range(0, len(matrix)):
        output += "\n"
        for j in range(0, len(matrix[i])):
            output += matrix[i][j]
    print(output)

def mirror_matrix():
    for i in range(20):
        matrix[i] += reversed(matrix[i])
    for i in range(19, 0, -1):
        matrix.append(matrix[i])


mirror_matrix()
print_matrix()

example output