Terry J. Reedy added the comment: Discussion continues because my close message was, I now realize, incomplete and therefore unsatisfying. Ditto for the doc. So I complete my close message here and reopen issue to augment the doc. The discussion has so far has glossed over the key question: "What is a legal section name?" Pulling the answer from the doc was a challenge. It uses 'legal section name', once, as if one should already know. Reading further, I found the answer: there is no (fixed) answer! The legal section name for a particular parser is determined by its .SECTCRE class attribute. '''configparser.SECTCRE A compiled regular expression used to parse section headers. The default matches [section] to the name "section".''' (This neglects to say whether the closing ']' is the first or last ']' on the line after the opening '['.) A non-verbose version of the default is re.compile(r"\[(?P<header>[^]]+)\]"). I propose adding near the top of the doc: "By default, a legal section name can be any string that does not contain '\n' or ']'. To change this, see configparser.SECTCRE." So my response to Miloš should have been to set SECTCRE to something like p below.

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p = re.compile(r"\[(?P<header>.*)\]") m = p.search("[Test[2]_foo]") m.group('header') 'Test[2]_foo'

Additional note: Postel's principle was formulated for internet protocols, which .ini files are not. In any case, it is not a Python design principle. Neither is "always check user input", which amounts to 'look before you leap'. So I will not debate these. However, "Errors should never pass silently." is #10 on the Zen of Python ('import this') and that I do attend to. ---------- assignee: -> docs@python components: +Documentation nosy: +docs@python resolution: rejected -> stage: test needed -> needs patch status: closed -> open versions: +Python 2.7, Python 3.4, Python 3.6 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue20923> _______________________________________