Description

assignee = None
closed_at = None
created_at = <Date 2013-04-24.15:06:00.650>
labels = ['type-bug']
title = 'csv.Sniffer.snif doesn\'t set up the dialect properly for a csv created with dialect=csv.excel_tab and containing quote (") char'
updated_at = <Date 2014-03-28.10:04:37.158>
user = 'https://bugs.python.org/GhislainHivon'

activity = <Date 2014-03-28.10:04:37.158>
actor = 'Antoon.Pardon'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2013-04-24.15:06:00.650>
creator = 'GhislainHivon'
dependencies = []
files = ['30001']
hgrepos = []
issue_num = 17829
keywords = []
message_count = 3.0
messages = ['187709', '214800', '215031']
nosy_count = 3.0
nosy_names = ['GhislainHivon', 'Antoon.Pardon', 'dmi.baranov']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue17829'
versions = ['Python 2.7', 'Python 3.2']

Activity

1. GhislainHivon commented on Apr 24, 2013

   

   GhislainHivonmannequin

   on Apr 24, 2013

   MannequinAuthor

   More actions

   When sniffing the dialect of a file created with the csv module with dialect=csv.excel_tab and one of the row contain a quote ("), the delimiter is set to ' ' instead of '\t'.
2. GhislainHivon

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Apr 24, 2013
3. AntoonPardon commented on Mar 25, 2014

   

   AntoonPardonmannequin

   on Mar 25, 2014

   Mannequin

   More actions

   I had a look at this and have the following remarks.

   1. the file csv_sniffing_excel_tab.py no longer works with python 3.3. It now produces the folowing traceback:

   Traceback (most recent call last):
     File "csv_sniffing_excel_tab.py", line 36, in <module>
       create_file()
     File "csv_sniffing_excel_tab.py", line 23, in create_file
       writer.writerows(test_data)
   TypeError: 'str' does not support the buffer interface

   2. The problem seems to be in the _guess_quote_and_delimiter method. If you always call _guess_delimiter, the sniffer give the correct result.

   3. As far as I understand the problem is the first regular expression:
      (?P<delim>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?P=delim)

   Now if we have a line as the following

   273:MVREGR1:ByEuPo:"Baryton ""Euphonium"" populaire"

   The delim group will match the space, the space group will match nothing the quote group will match " the non-group pattern will match "Euphonium" followed by the quote group matching " again and the delim group matching the space.

   And so we get the wrong delimiter.
4. AntoonPardon commented on Mar 28, 2014

   

   AntoonPardonmannequin

   on Mar 28, 2014

   Mannequin

   More actions

   I included a patch (against 2.7) that seems to make the test work.

   The patch prohibits the delim group to match a space.
5. ezio-melotti

   transferred this issue fromon Apr 10, 2022
6. serhiy-storchaka

   added this to CSV issues 📊on May 19, 2022
7. pradeepkumarai commented on Feb 23, 2023

   

   pradeepkumarai

   on Feb 23, 2023

   More actions

   I included a patch (against 2.7) that seems to make the test work.

   The patch prohibits the delim group to match a space.
8. arhadthedev

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Feb 25, 2023
9. serhiy-storchaka

   self-assigned this

   on Jan 9, 2024
10. serhiy-storchaka

    closed this as completedin #153694on Jul 21, 2026
11. github-project-automation

    moved this to Done in CSV issues 📊on Jul 21, 2026
12. serhiy-storchaka

    reopened this on Jul 21, 2026
13. serhiy-storchaka

    added

    3.13only security fixesonly security fixes

    3.14bugs and security fixesbugs and security fixes

    3.15bugs and security fixesbugs and security fixes

    on Jul 21, 2026
14. serhiy-storchaka commented on Jul 21, 2026

    

    serhiy-storchaka

    on Jul 21, 2026

    Member

    More actions

    Fixed in 3.16 by the csv.Sniffer rewrite (gh-83273). The old code counted every character adjacent to a quoted run and chose the most frequent one, so spaces around quotes inside fields could outnumber the real delimiter.

    The file from the original report is a Python 2 script, but the bug is still reproducible on 3.13 and 3.15:

    import csv, io
    rows = [['alpha', 'he said "hi" and "bye" then'],
            ['beta', 'she said "yes" or "no" maybe'],
            ['gamma', 'we said "up" and "down" too']]
    buf = io.StringIO()
    csv.writer(buf, dialect=csv.excel_tab).writerows(rows)
    print(repr(csv.Sniffer().sniff(buf.getvalue()).delimiter))  # ' ' instead of '\t'

    A targeted fix for the maintenance branches is welcome.
15. serhiy-storchaka

    removed their assignment

    on Jul 21, 2026

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