이렇게 하면 어떨까요?

a = "abcdefghijklm"

def split_by_for(s, n):
    result = []
    for i in range(0, len(s), n):
        result.append(s[i:i+n])
    return result

def split_by_list_comprehension(s, n):
    return [s[i:i+n] for i in range(0, len(s), n)]

def split_by_recursion(s, n):
    return [s[:n]] + split_by_recursion(s[n:], n) if s else []

split_by_rec_lambda = lambda s, n: [s[:n]] + split_by_rec_lambda(s[n:], n) if s else []

print(split_by_for(a, 3))
print(split_by_list_comprehension(a, 3))
print(split_by_recursion(a, 3))
print(split_by_rec_lambda(a, 3))