Python, I have a basic question.

From Python REPL

>>> # After this console
... # dotdotdot refers to the block of a function or specific syntax.

Therefore, ... must be followed by proper grammar written on the block.

However, a print("a") without an indent has arrived, so a syntax error occurs.

It's the same for REPL in other languages The role of REPL is to receive a single command and immediately output a return value or log message.

To see the multi-line code working at once, as you intended, You have to fill it out as a file and run it.