What can also be surprising is different behavior for quotechar="" and quotechar=None. I would make them behave the same (currently quotechar="" is not permitted), but it's very subjective indeed

It was. In the past, "" and "\0" were interpreted as None for delimiter, quotechar and escapechar. But it was confusing, and it was impossible to use the null character as the delimiter or whatever.

@serhiy-storchaka IIUC, quote_char=None is accepted for QUOTE_NONE, but quote_char="" is not, because there is a check that if it's a str, it must be a 1-char str. For me the fact that quote_char=None is accepted, but quote_char="" is not is strange (not talking here about the null character "\0", just about empty string)