Python - Crear matriz con caracteres aleatorios

for i in range (0,d):

    for j in range (0,d):

        test[i][j]=chr(random.randint(97,122))

ValueError: invalid literal for int() with base 10: 'a'

import random

d=5

test=[[0 for x in range(d)] for y in range(d)]

for i in range (0,d):

    for j in range (0,d):

        test[i][j]=chr(random.randint(97,122))

print(test)