Add a delimiters parameter to the csv.Sniffer constructor

Feature or enhancement

csv.Sniffer.sniff() accepts an optional delimiters argument which restricts the set of characters that can be guessed as a delimiter. has_header() has no such argument, so the restriction cannot be applied to it.

I propose to add an optional delimiters parameter to the constructor, so that it applies to the sniffer rather than to a single call:

sniffer = csv.Sniffer(',;\t')
if sniffer.has_header(sample):
    ...
dialect = sniffer.sniff(sample)

It is used by both sniff() and has_header(). The delimiters argument of sniff(), if given, still takes precedence.

The given delimiters are also preferred in that order if several of them split the sample equally well: csv.Sniffer(';,') guesses ';' where csv.Sniffer(',;') guesses ','.

Linked PRs

• gh-155060

まず、issue に記載されている csv.Sniffer、sniff()、has_header() のエントリポイントから始め、次に既存の CSV テストを調べて現在の動作を確認します。完了条件は、コンストラクターの delimiters 制限が両方のメソッドで使用され、sniff() がそれを上書きでき、同順位の候補が指定されたデリミタの順序に従うことです。