csv.DictWriter: inconsistency in handling of extrasaction arg

[akulakov]

BPO	44512
Nosy	@akulakov
PRs	bpo-44512: Fix handling of extrasactions arg with mixed or upper case #26924

^{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 2021-06-26.02:32:56.967>
labels = ['library', '3.9', '3.10', '3.11']
title = 'csv.DictWriter: inconsistency in handling of extrasaction arg'
updated_at = <Date 2021-06-27.16:11:26.461>
user = 'https://github.com/akulakov'

bugs.python.org fields:

activity = <Date 2021-06-27.16:11:26.461>
actor = 'andrei.avk'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-06-26.02:32:56.967>
creator = 'andrei.avk'
dependencies = []
files = []
hgrepos = []
issue_num = 44512
keywords = ['patch']
message_count = 1.0
messages = ['396536']
nosy_count = 1.0
nosy_names = ['andrei.avk']
pr_nums = ['26924']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue44512'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[akulakov]

In csv.DictWriter, the arg extrasaction case is handled inconsistently:

• if it's misspelled, e.g. ignor instead of 'ignore', a ValueError is raised by the __init__ method.

• if it's 'Ignore', 'IGNORE', it will work properly

• if it's 'raise', it will also work properly

• BUT: if it's 'Raise' or 'RAISE', it will have the same effect as 'ignore'

The code is here: https://github.com/python/cpython/blob/main/Lib/csv.py#L135-L146

[ins] In [1]: from csv import DictWriter

[ins] In [4]: d=DictWriter(open('testcsv','w'),'abc',extrasaction='IGNORE')

[ins] In [5]: list(d._dict_to_list(dict(d=1)))
Out[6]: ['', '', '']

[ins] In [7]: d=DictWriter(open('testcsv','w'),'abc',extrasaction='RAISE')

[ins] In [8]: list( d._dict_to_list(dict(d=1)) )
Out[8]: ['', '', '']

[ins] In [9]: d=DictWriter(open('testcsv','w'),'abc',extrasaction='TEST')
---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)
<ipython-input-9-953d1100c7f9> in <module>
----> 1 d=DictWriter(open('testcsv','w'),'abc',extrasaction='TEST')

/usr/local/Cellar/python@3.9/3.9.1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/csv.py in __init__(self, f, fieldnames, restval, extrasaction, dialect, *args, **kwds)
134 self.restval = restval # for writing short dicts
135 if extrasaction.lower() not in ("raise", "ignore"):
--> 136 raise ValueError("extrasaction (%s) must be 'raise' or 'ignore'"
137 % extrasaction)
138 self.extrasaction = extrasaction

ValueError: extrasaction (TEST) must be 'raise' or 'ignore'

[ins] In [10]: d=DictWriter(open('testcsv','w'),'abc',extrasaction='raise')

[ins] In [11]: list( d._dict_to_list(dict(d=1)) )
---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)
<ipython-input-11-1fde207e1805> in <module>
----> 1 list( d._dict_to_list(dict(d=1)) )

/usr/local/Cellar/python@3.9/3.9.1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/csv.py in _dict_to_list(self, rowdict)
147 wrong_fields = rowdict.keys() - self.fieldnames
148 if wrong_fields:
--> 149 raise ValueError("dict contains fields not in fieldnames: "
150 + ", ".join([repr(x) for x in wrong_fields]))
151 return (rowdict.get(key, self.restval) for key in self.fieldnames)

ValueError: dict contains fields not in fieldnames: 'd'

----
I propose to accept any case of Raise, RAISE, etc, to have the effect of 'raise'.

I can put up the PR if that sounds good.