These issues are not as simple as you think. But anyway, clearing the shell in #6143.
Shell is a modified editor. Currently, the arrows move the cursor around just as in the editor. For multiline statements, this is essential, and even for single-line statements, not as useless as some claim. Single-line command consoles can get away with changing the meaning of Up and Down. This is discussed in #2704, and what I said above is explained more in msg243140 of May 2015.
I have a question about Linux consoles. Windows Command Prompt is strictly a command *line* console. It sees
>>> def fib(n):
... if n >= 2:
... return fib(n-2) + fib(n-1)
... else:
... return n
as 5 commands. Its history mechanism retrieves a line at a time. Does a Linux console retrieve all 5 at once, as IDLE does?