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gh-150942: Speed up IOBase.readlines - #155304
demitryfly wants to merge 2 commits into
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| if (PyList_Append(result, line) < 0) { | ||
| Py_DECREF(line); | ||
| if (_PyList_AppendTakeRef((PyListObject *)result, line) < 0) { |
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The call to PyObject_Size(line) should be moved up. After the _PyList_AppendTakeRef we are no longer have a valid reference to line.
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| /* XXX special-casing this made sense in the Python version in order | ||
| to remove the bytecode interpretation overhead, but it could | ||
| probably be removed here. */ | ||
| PyObject *ret = PyObject_CallMethodObjArgs(result, &_Py_ID(extend), |
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The changes in this PR will not matter for calls like f.readlines() since that ends up in the fast path here. We could change the call here to PyObject_CallMethodOneArg which might be faster, but that is for another PR.
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| @@ -0,0 +1,2 @@ | |||
| Improve the performance of :meth:`io.IOBase.readlines` by avoiding | |||
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Can you provide benchmarks where this change has a positive effect for real-world cases? I suspect the change might be too minimal to warrant acceptance of the PR.
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This PR optimizes _io.IOBase.readlines() by using
_PyList_AppendTakeRef() when adding lines to the result list.
Previously, each line was added with PyList_Append(), which creates an
extra temporary reference. The new code transfers the existing reference
directly to the result list, avoiding an unnecessary reference-count
increment/decrement pair.
The order of operations is unchanged: the line is added before its length
is inspected, preserving the prior behavior.
Tests: