Cython: for i from 1 <= i < N

I'm learning Cython and came across this snippit of code:

import numpy as np
cimport numpy as np

def mean(np.ndarray[np.double_t] input):

    cdef np.double_t cur
    # Py_ssize_t is numpy's index type
    cdef Py_ssize_t i
    cdef Py_ssize_t N = len(input)

    for i from 0 <= i < N:
        cur += input[i]

    return cur / N

a=np.array([1,2,3,4], dtype=np.double)

Obviously, this returns the mean of a which is 2.5. My question is this:

Is the for loop a Python loop, Cython, or C?