But OP didn't type iterate_list either. Perhaps he saw little benefit on one and assumed the same would happen in the other. Cython's annotation mode (cython -a) doesn't really help either here, showing both OPs and optimized versions with a strong yellow color, indicating that they would be about the same, but compiling and trying both definitely shows the improvement.

Another funny thing: making a pure python version that uses the sum() built-in results in code that runs 80% as fast as the cython version, but also gives lower error (e-8 versus e-4 error that gets accumulated when the numbers are summed up one by one).