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GeezerVison is showing github.com — [3.11] gh-98820: Fix quadratic time in csv.Sniffer for quoted fields (GH-154867) by serhiy-storchaka · Pull Request #155538 · python/cpython

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@serhiy-storchaka

@serhiy-storchaka serhiy-storchaka commented Aug 11, 2026

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Manual backport of #154867, cherry-picked from the 3.12 backport (#155166).

It applies unchanged: 3.11 supports possessive quantifiers.

Sniffing '"abcdefghijklmnopqrstuvwxyz"\n' * n with delimiters=',:|\t' is now linear: 0.142, 0.286 and 0.569 s for n = 2500, 5000 and 10000.

  • Issue: csv.Sniffer().sniff() Hangs on Single-Column Data #98820

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@miss-islington @serhiy-storchaka
[3.11] pythongh-98820: Fix quadratic time in csv.Sniffer for quoted f…
5d4f953 
…ields (pythonGH-154867)

(cherry picked from commit b30c7fa)
(cherry picked from commit 39dac55)
@bedevere-app bedevere-app Bot mentioned this pull request Aug 11, 2026
csv.Sniffer().sniff() Hangs on Single-Column Data #98820
Closed
@bedevere-app bedevere-app Bot added the type-security A security issue label Aug 11, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Aug 11, 2026
[3.15] gh-98820: Fix quadratic time in csv.Sniffer for quoted fields #154867
Merged
@bedevere-app bedevere-app Bot added the awaiting core review label Aug 11, 2026
@pablogsal
pablogsal merged commit b09a67a into python:3.11 Aug 11, 2026
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@bedevere-app bedevere-app Bot removed the awaiting core review label Aug 11, 2026
@serhiy-storchaka
serhiy-storchaka deleted the backport-3.11-gh98820 branch August 27, 2026 12:13
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3 participants

@serhiy-storchaka @pablogsal @miss-islington
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