Dialect class defaults are not documented.

[MiK]

BPO	24147
Nosy	@smontanaro, @bitdancer, @berkerpeksag, @iritkatriel, @uniocto
PRs	bpo-24147: Document csv Dialect class defaults. Patch by Brandon Milam #25989
Files	sans_headers.csv quotebug.py csv_dialect_doc_clarify.patch: Document clarification csv.html: html file holding the changes

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2015-05-09.01:05:19.126>
labels = ['easy', 'type-bug', '3.10', 'docs']
title = 'Dialect class defaults are not documented.'
updated_at = <Date 2021-05-08.12:32:59.244>
user = 'https://bugs.python.org/MiK'

bugs.python.org fields:

activity = <Date 2021-05-08.12:32:59.244>
actor = 'uniocto'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2015-05-09.01:05:19.126>
creator = 'MiK'
dependencies = []
files = ['39328', '39406', '39552', '39553']
hgrepos = []
issue_num = 24147
keywords = ['patch', 'easy']
message_count = 14.0
messages = ['242787', '242807', '242811', '242818', '243396', '243397', '243399', '243402', '244344', '244347', '244400', '244407', '389327', '393254']
nosy_count = 8.0
nosy_names = ['skip.montanaro', 'r.david.murray', 'docs@python', 'berker.peksag', 'jbmilam', 'MiK', 'iritkatriel', 'uniocto']
pr_nums = ['25989']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue24147'
versions = ['Python 3.10']

Linked PRs

• gh-68335: Documenting csv dialect defaults #96842

[MiK]

Python 2.7.3 (default, Mar 13 2014, 11:03:55) 
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import csv
>>> class Mon(csv.Dialect):
...     delimiter = ','
...     quotechar = '"'
...     quoting = 0
...     lineterminator = '\n'
... 
>>> f = open('sans_headers.csv','r')
>>> reader = csv.DictReader(f, fieldnames=('code', 'nom', 'texte'), dialect=Mon)
>>> for l in reader:
...     print l
... 
{'nom': 'line_1', 'code': '3', 'texte': 'one line\ntwo lines'}
{'nom': 'line_2', 'code': '5', 'texte': 'one line\nand a quote "iop"";newline'}
{'nom': None, 'code': 'I\'m not a cat"', 'texte': None}
>>> f.seek(0)
>>> reader = csv.DictReader(f, fieldnames=('code', 'nom', 'texte'), delimiter=',', quotechar='"', quoting=0, lineterminator='\n')
>>> for l in reader:
...     print l
... 
{'nom': 'line_1', 'code': '3', 'texte': 'one line\ntwo lines'}
{'nom': 'line_2', 'code': '5', 'texte': 'one line\nand a quote "iop";newline\nI\'m not a cat'}
>>> 

If I use a subclass of csv.Dialect with the same attribute that I should use with keywords in calling csv.DictReader I don't get the same behaviour.

[smontanaro]

Can you attach your cab file so we don't need to reconstruct it (and possibly make a mistake) by reading your program's output?

[smontanaro]

Sorry, failed to override my phone's spell correction. "cab" should be
"csv".

[MiK]

Hi,

This is the file used for my test.

Thank you,

regard,

Mik

[smontanaro]

In your Mon class, you've left the doublequote parameter unset (it defaults to None). It completely overrides the default dialect. When no Dialect class is given, the default is csv.excel. Note that doublequote is set to True in csv.excel. In your second example, the reader starts with csv.excel, then selectively overrides the named attributes.

[MiK]

Ok Thanks.

But perhaps the documentation of csv.Dialect would be updated with the default parameters. If all attribute may be specified this would be indicated in the doc.

[bitdancer]

Yes, I think the documentation should be improved.