shouty.py

# Trio program that reads from stdin, uppercases everything, and then echoes
# it back to stdout.

# This uses some internal APIs, because Trio v0.7.0 doesn't have a real public
# API for talking to stdin/stdout yet. This only works on Unix.
# If you want to help implement a real API for this, or just check whether
# anything new has happened, see:
#     https://github.com/python-trio/trio/issues/174

import trio
# Temporary hack until Trio has a real API for this:
from trio._subprocess.unix_pipes import PipeSendStream, PipeReceiveStream

async def main():
    stdin = PipeReceiveStream(0)
    stdout = PipeSendStream(1)
    stream = trio.StapledStream(stdout, stdin)

    while True:
        data = await stream.receive_some(9999) # arbitrary buffer size
        if not data:
            break
        await stream.send_all(data.upper())

trio.run(main)

Example (lowercase is what I typed, uppercase is printed by the program):

~$ python shouty.py 
hello
HELLO
can you hear me
CAN YOU HEAR ME