[docs] [issue15840] Ambiguity with regard to the effect of accessing a closed IOBase instance

[Antoine Pitrou]

Antoine Pitrou added the comment:

> 1) IOError and ValueError are not subclasses one of another. So what
> should we expect an IOBase implementation to raise?

Ideally, ValueError should be raised, but I suspect some methods raise IOError instead.

> Undefined behavior means literally anything can happen.

In practice, it will either raise an error, or be ignored. For example, calling close() a second time would be ignored. Calling readable() may return the original value (before the file was closed), etc.

Any non-trivial behaviour should be reported as a bug, though. Especially, reading or writing methods (read(), write(), readline() etc.) should *never* succeed on a closed file.

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components: +IO
nosy: +pitrou
stage:  -> needs patch
versions: +Python 3.2, Python 3.3

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