Follow-up from "Draft: Resolve "Create a session manager""

The following discussion from !49 (merged) should be addressed:

• @ba0506 started a discussion: (+6 comments)

  There are a few observations I would like to mention: i) A statement such as print(3) returns "None" in the Output. I think it should return 3. ii) The name run_session seems more intuitive to me than run_loop

  Some inconsistent behavior: iii) After the Input 3 + 5, the Output is 8. Then, after the next Input b = 3, a "RuntimeError is raised (see attached png) ... In putting b = 3 as the first statement or reverting the above two does not raise any error. iv) a = 1 returns nothing in the Output. Inputting a = 2 afterwards returns None, since the value of a was repeatedly set.