Transmitting sketches to Yun with Autobahn - a byte at a time?
Partial answer: to send more information than just a single byte, it is possible to run:

# python
payload = "Here is a longer string"

# arduino
String commands = port-&gt;readString();           // Reads the whole thing
String commands = port-&gt;readStringUntil('\n');  // Reads until the given separator