viirya commented on PR #50327: URL: https://github.com/apache/arrow/pull/50327#issuecomment-4861011814
Good idea — I tried exactly that (`cdef list result = [None] * n` + indexed assignment, also letting null rows keep the prefilled `None`), but it benchmarks the same or slightly worse: `list<string>` 0.34 s → 0.35–0.37 s, `list<list<int32>>` 0.65 s → 0.69–0.70 s (best of 3, consistent across reruns). Two reasons, I think: Cython already lowers `result.append(x)` on a local it can see is a list to a `PyList_Append` call, and CPython lists over-allocate geometrically, so the resize cost is amortized and tiny. Meanwhile the preallocated version pays an extra refcount round-trip per slot (every `result[i] = x` has to decref the prefilled `None`). The loops are dominated by creating the per-row slice objects / decoding UTF-8 either way, so I kept the simpler `append` form. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
