It’s a REPL, for starters.
A REPL, by its name, is a very narrow version of the broader paradigm of interactive computer programming environments. But Notebooks are not REPLs, unless you use REPL to mean "interactive programming environment" and not REPL. Notebooks are much broader than a REPL! In a notebook, you can go back and edit and run individual lines of the notebook without re-running the whole notebook from the start and without re-computing everything that depends on what you just edited. Behavior like this makes it super hard to track the actual state, and super easy to lose track of how things are how they are. That's pretty terrible!
The parent article links this great talk that goes into more detail than the parent post and is much easier to understand: https://www.youtube.com/watch?v=7jiPeIFXb6U
Isn't this a standard on REPLs as well? You can select the code you wish to run, and press Ctrl+Enter or what ever. I must admit, I've programmed Python for about 10 years in Spyder and VS Code now, but I haven't used notebooks at any point. Just either ad-hoc scripts or actual source files.
My definition of a "notebook" is an ad-hoc script, split into individual "cells" which are typically run as a whole. On my workflow, I just select the code I wish to run. Sometimes it is one expression, one line, 100 lines or 1000 lines depending what I've changed on the script.
Not usually, no. Type `python` at the command prompt - what you get is a REPL. Type `clisp` at the command prompt, or `wish`, or `psql`, or `perl` or even `bash` - those are al REPLs.
Very different to a program that presents an editor, and then lets the user selectively choose which lines/expressions in that editor to run next. For example, type `emacs somefile.sql` in the command prompt. The application that opens is most definitely not a READ-EVAL-PRINT-LOOP.
For the same reason that adding (working) wings to a car makes it not a car anymore.[1]
I mean, to my mind, when something is satisfying a different primary use-case, then that thing is a different thing.
I'm sure there's some fuzziness in the distinction between "This is a REPL/car and this is a Notebook/plane".
Usually it's very easy to see the distinction - the REPL is waiting for the next command and the next command only while the notebook takes whatever input you give it, determines whether it got a command or content, and reacts appropriately.
[1] Tons of examples, TBH. I don't refer to my computer as my calculator, even though the computer does everything a fancy calculator can do. People don't call motorcycles 'bicycles', even though the motorcycle can go anywhere that a legal bicycle can go. More telling is how people don't call their computer monitor 'TV' and don't call the TV a 'Monitor' even when the same actual item is used for both (i.e. I repurposed an old monitor as a small-screen netflix-box, and now an item that used to be called 'monitor' by wife and kids is called 'TV' by wife and kids).
Jupyter Notebook absolutely is a REPL, see my sibling comment above for the WP link describing it as such. It waits for input, then evals the input, the prints the return value, and then loops.
“A Jupyter Notebook application is a browser-based REPL containing an ordered list of input/output cells which can contain code, text (using Github Flavored Markdown), mathematics, plots and rich media.”