cpython vs cython vs numpy array performance

Question

I am doing some performance test on a variant of the prime numbers generator from http://docs.cython.org/src/tutorial/numpy.html. The below performance measures are with kma

Answer 1

why is the numpy array so incredibly slower than a python list, when running on CPython?

Because you didn't fully type it. Use

cdef np.ndarray[dtype=np.int, ndim=1] p = np.empty(kmax, dtype=DTYPE)

how do I cast a numpy array to a int*?

By using np.intc as the dtype, not np.int (which is a C long). That's

cdef np.ndarray[dtype=int, ndim=1] p = np.empty(kmax, dtype=np.intc)

(But really, use a memoryview, they're much cleaner and the Cython folks want to get rid of the NumPy array syntax in the long run.)