From 3f7cc33efb58c84ad93d8f2f36490c823c2e777f Mon Sep 17 00:00:00 2001 From: Serhiy Storchaka Date: Wed, 22 Jul 2026 15:20:08 +0300 Subject: [PATCH 1/2] [3.14] gh-80678: Document the preferred delimiters of csv.Sniffer (GH-154336) The delimiters which win when several combinations fit the sample equally well were not documented. (cherry picked from commit 79cdcee308c6612edd6d1ca972342e2a088b6b4e) Co-authored-by: Serhiy Storchaka Co-authored-by: Claude Opus 4.8 (1M context) --- Doc/library/csv.rst | 5 +++++ Lib/csv.py | 4 ++++ 2 files changed, 9 insertions(+) diff --git a/Doc/library/csv.rst b/Doc/library/csv.rst index 1eb3fe0d490353..746d70329751a0 100644 --- a/Doc/library/csv.rst +++ b/Doc/library/csv.rst @@ -314,6 +314,11 @@ The :mod:`!csv` module defines the following classes: is given, it is interpreted as a string containing possible valid delimiter characters. + If several combinations fit the sample equally well --- + for example if both ``','`` and ``';'`` split every row consistently --- + the delimiters ``','``, ``'\t'``, ``';'``, ``' '`` and ``':'`` + are preferred, in this order, + no matter how many times each of them occurs. .. method:: has_header(sample) diff --git a/Lib/csv.py b/Lib/csv.py index 6efa889ed84677..843c2e38727329 100644 --- a/Lib/csv.py +++ b/Lib/csv.py @@ -243,6 +243,10 @@ def __init__(self): def sniff(self, sample, delimiters=None): """ Returns a dialect (or None) corresponding to the sample + + If several combinations fit the sample equally well, the + delimiters listed in the preferred attribute are preferred, in + that order, no matter how many times each of them occurs. """ quotechar, doublequote, delimiter, skipinitialspace = \ From df9c34a463afc54d5447e63dce2738dd3801710c Mon Sep 17 00:00:00 2001 From: Serhiy Storchaka Date: Sun, 26 Jul 2026 21:40:19 +0300 Subject: [PATCH 2/2] Say 'delimiters', not 'combinations' The maintenance branches do not deduce the dialect by trying combinations of parameters, so only the delimiter candidates can tie. --- Doc/library/csv.rst | 2 +- Lib/csv.py | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/Doc/library/csv.rst b/Doc/library/csv.rst index 746d70329751a0..64065a75917af8 100644 --- a/Doc/library/csv.rst +++ b/Doc/library/csv.rst @@ -314,7 +314,7 @@ The :mod:`!csv` module defines the following classes: is given, it is interpreted as a string containing possible valid delimiter characters. - If several combinations fit the sample equally well --- + If several delimiters fit the sample equally well --- for example if both ``','`` and ``';'`` split every row consistently --- the delimiters ``','``, ``'\t'``, ``';'``, ``' '`` and ``':'`` are preferred, in this order, diff --git a/Lib/csv.py b/Lib/csv.py index 843c2e38727329..92bb9b55a4d3eb 100644 --- a/Lib/csv.py +++ b/Lib/csv.py @@ -244,7 +244,7 @@ def sniff(self, sample, delimiters=None): """ Returns a dialect (or None) corresponding to the sample - If several combinations fit the sample equally well, the + If several delimiters fit the sample equally well, the delimiters listed in the preferred attribute are preferred, in that order, no matter how many times each of them occurs. """