[Python-Dev] Fuzziness in io module specs (original) (raw)
Pascal Chambon chambon.pascal at gmail.com
Fri Sep 18 21:17:29 CEST 2009
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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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