For the small cases (say n < 50), we can get faster code by using a small (3Kb) table of factorial logarithms:

   double lf[50] = [log2(factorial(n)) for n in range(50)];

Then comb() and perm() can be computed quickly and in constant time using the C99 math functions:

   result = PyLong_FromDouble(round(exp2(lf[n] - (lf[r] + lf[n-r]))));