polymult.py

def polymult(a, b):
    exp = 10

    ares = 0 # evaluate a at x
    for ac in a:
        ares = (ares<<exp) + ac

    bres = 0 # evaluate b at x
    for bc in b:
        bres = (bres<<exp) + bc

    prod = ares * bres
    result = []
    while prod != 0:
        if prod&(1<<(exp-1)): # if flag bit is set
            result.append(-((~prod+1)&(1<<exp)-1))
            prod += 1<<exp # tfw 2s compliment
        else:
            result.append(prod & (1<<exp)-1)
        prod = prod>>exp

    return result

print(polymult([6,-6,-5],[7,6,-5]))