[Python-Dev] Fuzziness in io module specs

[Guido van Rossum]

Why not propose an update to the existing PEP to clarify the vaguenesses?

On Fri, Sep 18, 2009 at 12:17 PM, Pascal Chambon
<chambon.pascal at gmail.com> wrote:
> Hello everyone
>
> I'm currently working on a reimplementation of io.FileIO, which would allow
> cross-platform file range locking and all kinds of other safety features ;
> however I'm slightly stuck due to some specification fuzziness in the IO
> docs.
> CF     http://bugs.python.org/issue6939
>
> The main points that annoy me at the moment :
> - it is unclear what truncate() methods do with the file pointer, and even
> if the current implementation simply moves it to the truncation point, it's
> very contrary to the standard way of doing under unix, where the file
> pointer is normally left unchanged. Shouldn't we specify that the file
> pointer remains unmoved, and fix the _fileio module accordingly ?
> - exceptions are not always specified, and even if most of them are
> IOErrors, weirdly, in some cases, an OSError is raised instead (ie, if we
> try to wrap a wrong file descriptor when instanciating a new FileIO). This
> might lead to bad program crashes if some people don't "refuse the
> temptation to guess" and only get prepared to catch IOErrors
> - the doc sometimes says that when we receive an empty string from a read()
> operation, without exceptions, it means the file is empty. However, with the
> current implementation, if we call file.read(0), we simply receive "", even
> though it doesn't mean that we're at EOF. Shouldn't we avoid this (rare, I
> admit) ambiguity on the return value, by preventing read(0) ? Or at least,
> note in the doc that (we receive an empty string) <-> (the file is at EOF OR
> we called read with 0 as parameter) ?
>
> Are there some arguments that I don't know, which lead to this or that
> particular implementation choice ?
> I'd strongly advocate very detailled specifications, letting no room for
> cross-platform subtilities (that's also a strong goal of my
> reimplemntation), since that new IO system (which saved me a lot of coding
> time, by the way) should become the base of many programs.
>
> So wouldn't it be a godo idea to write some kind of mini-pep, just to fix
> the corner cases of the current IO documentation ? I might handle it, if no
> more-knowledgeable people feels like it.
>
> Regards,
> Pascal
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-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)