gh-138005: Document that CSV skipinitialspace=True and delimiter=' ' require quotation for empty fields

[maurycy]

Please see for the code:

• cpython/Modules/_csv.c

  Lines 1253 to 1267 in 7dc42b6

  	if (!field_len && dialect->delimiter == ' ' && dialect->skipinitialspace) {
  	if (dialect->quoting == QUOTE_NONE ||
  	(field == NULL &&
  	(dialect->quoting == QUOTE_STRINGS ||
  	dialect->quoting == QUOTE_NOTNULL)))
  	{
  	PyErr_Format(self->error_obj,
  	"empty field must be quoted if delimiter is a space "
  	"and skipinitialspace is true");
  	return 0;
  	}
  	quoted = 1;
  	}
  	rec_len = join_append_data(self, field_kind, field_data, field_len,
  	&quoted, 0);

Please see the test:

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

The behavior is intentional since gh-115721, so the only sensible route is to update the docs.

• Issue: Document that CSV skipinitialspace=True and delimiter=' ' require quotation for empty fields #138005

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📚 Documentation preview 📚: https://cpython-previews--138006.org.readthedocs.build/

[serhiy-storchaka]

I think this is too verbose. The note takes up a lot of space and attracts a disproportionate amount of attention. Most users will never encounter this, and if they do, this behavior is expected and therefore does not require any special explanation.

Could you please limit yourself to one short sentence? That such CSV files cannot contain empty fields.

[maurycy]

I think this is too verbose. The note takes up a lot of space and attracts a disproportionate amount of attention. Most users will never encounter this, and if they do, this behavior is expected and therefore does not require any special explanation.

Could you please limit yourself to one short sentence? That such CSV files cannot contain empty fields.

Thank you for taking a look. Made it much shorter:

• https://github.com/python/cpython/pull/138006/files#diff-863b8cdc270a710deec9ffcf11f82fe2547cd96e8d935e37361b431a5accd3f3R470-R471

[serhiy-storchaka]

LGTM. 👍

[sharktide]

LGTM
And thanks for fixing the typo :)