Decart

t = [[1, 2, 3], ['a', 'b', 'c'], ['_1', '_2', '_3'], ['_a', '_b', '_c']]

def dec(a, b):
    buf = [[]]
    e = 0
    for i in a:
        for j in b:
            if not isinstance(i, list): i = [i]
            if not isinstance(j, list): j = [j]
            buf[e] = i + j
            if not e == len(a) * len(b) - 1:
                buf.append([])
            e += 1
    return buf

g = dec(t[0], t[1])
for i in t[2:]:
    g = dec(g, i)