Find the factors by trying numbers

A whole-number zero of a polynomial with whole-number coefficients, and $1$ in front of the top power, must divide the constant term. You will list the divisors, test them, and write the factors.

The idea. Test each divisor $d$ of the constant term, and also $-d$. Every one that gives $p = 0$ is a zero, and $x - d$ is a factor.

Your tasks.

1. In divisors, return the positive divisors of n, using its size abs(n).
2. In whole_zeroes, return the sorted list of whole-number zeroes.
3. Set zeroes for $x^3 - 2x^2 - 11x + 12$.