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Comment by dr_zoidberg | Hacker News Reader

OP has an open pull request on his repo[0] where someone made basically this same change (different names for the variables, but same idea).

According to OP, he tried this but it resulted in slower execution for him. I'm not sure he really followed what that PR says. In the case of the submitter, it says on their machine it gave a 2x speedup (smaller than my ~7x, but still significant).

[0] https://github.com/00sapo/cython_list_test/pull/3

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If you carefully read OP's response in the PR, he says he tried static typing make_list in addition to iterate_list. Your comment elides the resource allocation step.

Like OP, I observed that static typing make_list yields little benefit. It's runtime is 3x the runtime of iterate_list. And that makes sense. I'm not sure why we'd expect Cython to speed up the allocation of large numbers of Python objects.

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).

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