[New-bugs-announce] [issue44861] csv.writer stopped to quote values with escapechar with csv.QUOTE_MINIMAL in Python 3.10

[Sebastian Bank]

New submission from Sebastian Bank <sebastian.bank at uni-leipzig.de>:

AFAICT there was an undocumented change in behaviour related to the fix of https://bugs.python.org/issue12178 (also reported in https://bugs.python.org/issue12178#msg397440):

Python 3.9 quotes values with escapechar:

```
import csv
import io

kwargs = {'escapechar': '\\'}

value = 'spam\\eggs'

print(value)

with io.StringIO() as buf:
    writer = csv.writer(buf, **kwargs)
    writer.writerow([value])
    line = buf.getvalue()

print(line.strip())

with io.StringIO(line) as buf:
    reader = csv.reader(buf, **kwargs)
    (new_value,), = reader

print(new_value)
spam\eggs
"spam\eggs"
spameggs
```

- quotes escapechar
- fails to double the escapechar (https://bugs.python.org/issue12178)

>From https://docs.python.org/3/library/csv.html#csv.QUOTE_MINIMAL

> only quote those fields which contain special characters
> such as delimiter, quotechar or any of the characters in
> lineterminator.

The previous behaviour seems incorrect because escapechar is not explicitly mentioned, but at the same time the docs says 'such as'.

The new might better matching the name 'minimal', but at the same time one might regard 'quote when in doubt' as a safer behaviour for the default quoting rule.

Python 3.10:

https://github.com/python/cpython/blob/5c0eed7375fdd791cc5e19ceabfab4170ad44062/Lib/test/test_csv.py#L207-L208

See also https://github.com/xflr6/csv23/actions/runs/1027687524

----------
components: Library (Lib)
messages: 399188
nosy: ebreck, taleinat, xflr6
priority: normal
severity: normal
status: open
title: csv.writer stopped to quote values with escapechar with csv.QUOTE_MINIMAL in Python 3.10
type: behavior
versions: Python 3.10

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue44861>
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