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gh-156748 : Performance - Use takeref append in _csv by brittanyrey · Pull Request #156749 · python/cpython · GitHub

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gh-156748 : Performance - Use takeref append in _csv - #156749

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gh-156748 : Performance - Use takeref append in _csv#156749
brittanyrey wants to merge 2 commits into
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brittanyrey:b-perf-csv-append-takeref

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brittanyrey commented Aug 31, 2026 •
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Reduce refcount churn by consuming the reference instead in lieu of calling append and decreffing.

Benchmark base patched delta
50 fields × 200 rows 537.7 µs 508.3 µs −5.5%
quoted + embedded separators/newlines 468.9 µs 435.8 µs −7.1%
all-empty fields (50 × 200) 173.6 µs 150.0 µs −13.6%
2 fields × 200 rows 24.0 µs 23.3 µs −2.9% (noise 3.3%)
5 × 500-char fields (control) 2517.7 µs 2508.2 µs −0.4% (noise 21%) 
# 50 fields x 200 rows
data = "\n".join(",".join(f"f{j}" for j in range(50)) for _ in range(200))
list(csv.reader(io.StringIO(data)))

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aisk reviewed Sep 1, 2026
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Comment thread Misc/NEWS.d/next/Core_and_Builtins/2026-09-01-03-05-22.gh-issue-156748.B0Z47w.rst
@@ -0,0 +1 @@
Optimize refcount churn in _csv.

aisk Sep 1, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

This should be in the Library folder. And refcount churn is not a user-observable detail, I think we should just mention the performance optimization.

aisk commented Sep 1, 2026

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I ran the benchmarks on my machine (MacBook Air with M3 chip) and got similar results:

Benchmark base patched delta PR
50 fields × 200 rows 408.5 µs 389.9 µs −4.6% −5.5%
quoted + embedded sep/newlines 725.3 µs 707.6 µs −2.4% −7.1%
all-empty fields (50 × 200) 115.8 µs 105.5 µs −8.9% −13.6%
2 fields × 200 rows 16.5 µs 16.1 µs −2.6% −2.9%
5 × 500-char fields (control) 2288.6 µs 2282.8 µs −0.3% −0.4%

eendebakpt commented Sep 1, 2026

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This is a duplicate of #150995. I will close in favor of the earlier PR.

eendebakpt closed this Sep 1, 2026
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