CSV Writer Regression in Python 3.11+: Escaping Required but Unnecessary

[cspurk]

Bug report

Bug description:

The following csvtest.py script works for Python 3.10 and earlier but fails for 3.11 and later:

import csv
import io
b = io.StringIO()
csv.writer(b, quoting=csv.QUOTE_NONE, lineterminator='\n').writerow(["\r"])
print(repr(b.getvalue()))

For example, running the shell script …

for v in 9 10 11 12 13; do
    pyenv shell 3.$v
    python --version
    python csvtest.py
done

… yields:

Python 3.9.21
'\r\n'
Python 3.10.16
'\r\n'
Python 3.11.11
Traceback (most recent call last):
  File "/tmp/csvtest.py", line 4, in <module>
    csv.writer(b, quoting=csv.QUOTE_NONE, lineterminator='\n').writerow(["\r"])
_csv.Error: need to escape, but no escapechar set
Python 3.12.8
Traceback (most recent call last):
  File "/tmp/csvtest.py", line 4, in <module>
    csv.writer(b, quoting=csv.QUOTE_NONE, lineterminator='\n').writerow(["\r"])
_csv.Error: need to escape, but no escapechar set
Python 3.13.1
Traceback (most recent call last):
  File "/tmp/csvtest.py", line 4, in <module>
    csv.writer(b, quoting=csv.QUOTE_NONE, lineterminator='\n').writerow(["\r"])
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^
_csv.Error: need to escape, but no escapechar set

As in Python 3.10 and earlier, escaping the carriage return character (\r) should not be necessary (due to the custom lineterminator), but Python 3.11+ still expects it.

CPython versions tested on:

3.9, 3.10, 3.11, 3.12, 3.13

Operating systems tested on:

Linux