Document that CSV `skipinitialspace=True` and `delimiter=' '` require quotation for empty fields

[maurycy]

skipinitialspace=True and delimiter=' ' raise an exception for an unquoted blank field:

• https://github.com/python/cpython/pull/115721/files#diff-dd5e5efc1566b1c1dc988769a04cc403d2416c8af5bf4785bec235d02a780813R352-R354

The docs do not mention this behavior:

• https://docs.python.org/3/library/csv.html#csv.Dialect.skipinitialspace

Simple demonstration:

>>> import csv, io
>>> buf = io.StringIO()
>>> w = csv.writer(buf, delimiter=' ', skipinitialspace=True, quoting=csv.QUOTE_NONE)
>>> w.writerow(['', 'x'])
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    w.writerow(['', 'x'])
    ~~~~~~~~~~^^^^^^^^^^^
_csv.Error: empty field must be quoted if delimiter is a space and skipinitialspace is true

This is since gh-115721. The behavior is intentional and the docs should be updated.

Linked PRs

• gh-138005: Document that CSV skipinitialspace=True and delimiter=' ' require quotation for empty fields #138006
• [3.14] gh-138005: Document that CSV skipinitialspace=True and delimiter=' ' require quotation for empty fields (GH-138006) #138798
• [3.13] gh-138005: Document that CSV skipinitialspace=True and delimiter=' ' require quotation for empty fields (GH-138006) #138799

[hugovk]

Thanks!