In Python 3, pickle accepts to serialize a file object, but the result is nonsensical when unpickled. I think we should explicitly forbid pickling of FileIO, Buffered{Reader,Writer} and TextIOWrapper objects.

Sounds like a good idea to me.

Here is a patch, but issue10173 must probably be fixed first.

The patch modifies _io.TextIOWrapper, but not _pyio.TextIOWrapper. Is there a reason?

> The patch modifies _io.TextIOWrapper, but not _pyio.TextIOWrapper. Is
> there a reason?

Yes, two of them:
- modifying _pyio.Buffered* is enough to trigger the TypeError
- _pyio.StringIO inherits from TextIOWrapper, and it must be pickleable

I don't see why Buffered or TextIO's shouldn't be pickleable, ISTM their pickleability should be based on what the underlying file obj is.

What would be the use case for that?

> I don't see why Buffered or TextIO's shouldn't be pickleable, ISTM
> their pickleability should be based on what the underlying file obj
> is.

That could be. Right now, though, pickling them gives nonsensical
results and I think it would be better to give an explicit error
message.

(a problem with making them pickleable is that, by exposing details of
the internal structure in the pickle, you're limiting what
implementation changes you can do in the future)

Committed in r86220. I won't backport it since it would risk breaking existing code, although relying on this is really a bug in itself.