Improve performance by using reference stealing methods

[eendebakpt]

Feature or enhancement

Proposal:

We can improve performance of cpython by using stealing methods (_PyList_AppendTakeRef, _PyDict_SetItem_Take2, PyTuple_FromPairSteal etc.) instead of the normal ones. Using stealing methods we typically avoid an incref/decref pair and sometimes error handling is simplified. We should only make changes where it makes a performance impact, the code is not more complex and the modules or methods affected are performance critical.

A list of possible cases (there might be more). The issue is open for anyone to work on.

Location	Module / context	Helper
Modules/_csv.c:688	csv reader, per field	_PyList_AppendTakeRef
Modules/pyexpat.c:472	pyexpat StartElement, per attribute	_PyDict_SetItem_Take2
Modules/_elementtree.c:3351	ElementTree C accel attrib dict	_PyDict_SetItem_Take2
Modules/_io/bytesio.c:577	io.BytesIO.readlines	_PyList_AppendTakeRef
Modules/_io/iobase.c:756	io.IOBase.readlines (generic)	_PyList_AppendTakeRef
Objects/frameobject.c:639 & 658	frame f_locals / vars() / tracing	_PyList_AppendTakeRef
Modules/_pickle.c:5138	pickle Pickler memo copy	_PyDict_SetItem_Take2
Modules/_io/textio.c:2337 & 2343	io.TextIOWrapper readline (multi-chunk)	_PyList_AppendTakeRef
Modules/_asynciomodule.c:1213	asyncio future done-callback compaction	_PyList_AppendTakeRef

Linked PRs

• gh-150942: Speed up re.findall and re.sub/subn result building #150943
• gh-150942: Speed up json.loads array and object decoding #150945

[omkar-334]

hi @eendebakpt @StanFromIreland can i work on a module , maybe csv or textio

[eendebakpt]

hi @eendebakpt @StanFromIreland can i work on a module , maybe csv or textio

Sure! Try out, benchmark, test. If benchmarks show significant improvements you can open a PR, if not just report here briefly.