zljubisic at gmail.com wrote at 2020-5-23 04:24 -0700: >I have to talk to outer system by stdin/stdout. >Each line that comes to stdin should be processed and its result returned back to stdout. Logging should go to stderr. > >How to design a class that will listed to stdin and call required methods in order to process the data? Start by reading the Python tutorial ("https://docs.python.org/3/tutorial/index.html#tutorial-index"), especially section 7.