While writing tests for nntplib, it came to me that a PipeIO or BytesPipeIO would be useful (I actually wrote a minimal one). It would be a non-seekable in-memory bytes buffer with distinct read and write pointers, so as to act like a system FIFO or a socket.makefile() object. A pure Python implementation would probably be sufficient, since the main use would be for test purposes. What do you think?

(you may point to os.pipe() but it has problems such as limited buffer size: try to write many bytes to the write end and it will block until the other end tries to read something)