Python code to make a n-back sequence of 9 letters of length 36

make_n_back.py

import string
from random import choice

letters = list(string.ascii_uppercase[:9])

n = 2
K = 36

stimuli = [None] * K
response = [None] * K
for i in range(K):
    if i < n:
        stimuli[i] = choice(letters)
    else:
        if choice([True, False]):
            stimuli[i] = stimuli[i-2]
            response[i] = 'same'
        else:
            while True:
                stimuli[i] = choice(letters)
                if stimuli[i] != stimuli[i-2]:
                    break
            assert stimuli[i] != stimuli[i-2]
            response[i] = 'different'

# look at the stimuli and the correct responses 
list(zip(stimuli, response))