For compatibility, I think it may be good to add custom implementations of the buffer attribute and detach() method to stdin/out. They should be able to at least read and write ASCII bytes. It might be easiest to keep them as the current BufferedReader/Writer objects. Probably also make stdin/out.fileno() defer to the buffer attribute.

With the current patch that only allows reading and writing in UTF-16 pairs, I forsee a few problems:

* I assume stdin.buffer.raw.readline() will try to read one byte at a time, and will therefore always indicate EOF.
* Incompatibility with using stdin/out.buffer for ASCII character input and output. I suggest testing the patch with “python -m base64”, a use case mentioned earlier in this thread.