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

Comece pelos pontos de entrada csv.Sniffer, sniff() e has_header() descritos na issue e, em seguida, inspecione os testes CSV existentes para verificar o comportamento atual. Está concluído quando a restrição delimiters do construtor é usada por ambos os métodos, sniff() pode sobrescrevê-la e candidatos empatados seguem a ordem de delimitadores fornecida.