>>> next(csv.reader([r'2\.5'], escapechar='\\', quoting=csv.QUOTE_NONNUMERIC))
[2.5]
>>> next(csv.reader([r'.5'], escapechar='\\', quoting=csv.QUOTE_NONNUMERIC))
[0.5]
>>> next(csv.reader([r'\.5'], escapechar='\\', quoting=csv.QUOTE_NONNUMERIC))
['.5']

It parses numbers with an escaped character in the middle, it parses numbers starting with a dot, but it does not parse numbers starting with an escaped character. The following variants would be more consistent:

1. Any escaped character disables parsing field as a number.
2. Allow parsing a field starting with an escaped character as a number.

Linked PRs

• gh-113785: csv: fields starting with escapechar are not quoted #122110
• [3.13] gh-113785: csv: fields starting with escapechar are not quoted (GH-122110) #122258
• [3.12] gh-113785: csv: fields starting with escapechar are not quoted (GH-122110) #122259