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

IIUC there is no way to work around this from client/downstream code (to get the olf 3.6 to 3.9 behaviour), so this might break assertions on the output of `csv.writer` for users of `escapechar` whenever the data to be written contains the escapcechar (e.g. calculating a hash/checksum).

The 3.9 behavior is incorrect: write 'spam\\eggs', read 'spameggs'. The 3.10 behavior is correct: write 'spam\\eggs', read 'spam\\eggs'. What is your problem exactly?

The 3.9 behaviour is write: "spam\eggs"

The 3.10 behaviour is write: spam\\eggs

I think at least the change in csv.QUOTE_MINIMAL behviour should be documented (maybe adding hint to avoid the `escapechar` option for consistent output).