3 ms·

I never understood this > >>> exit > Use exit() or Ctrl-D (i.e. EOF) to exit If it knows we want to exit, why not just do it facepalm emoji

dmart 3y ago
There’s a sense in which it’s pedantically correct - ‘exit’ (and ‘help’) are not Python keywords outside of the REPL, so a beginner might try to use it in a script (maybe like sys.exit()?) and be confused. But I think the convenience is worth it.
- mariocesar 2y ago
  Yes, but it goes against the principles of "Explicit is better than implicit" and "There should be one-- and preferably only one—-obvious way to do it." We use parentheses () to call a function. print was a keyword in Python2, now, with print(), it's clear that we are calling for the execution. It's fun because `exit` alone in the REPL will return an object, and you can get the `exit.eof`, where is the message of what the keyword shortcut to call exit is, and it changes depending on the OS.
OutOfHere 3y ago
That's because `exit` will never work in a script, but `exit()` can.
- mariocesar 3y ago
  note that `exit()` on a script will also not work, as the exit function is only loaded on REPL. To make it work on a script, you will need to import the sys package and later call sys.exit()
  - OutOfHere 2y ago
    `exit()` absolutely works in a script assuming that the `site` module was not bypassed at startup via `python -S`. I understand that `sys.exit()` and others are preferred.
mariocesar 3y ago
I think there's a bit of a misunderstanding regarding exit. exit is not a keyword or a REPL command, it's actually a function exposed in the builtin package. you can run "import builtins; builtins.exit()" and see that is there To clarify, there are two things here: why exit exists in the REPL, and why it's a function. The exit() function is available only in the REPL, and it appears built-in, but it isn't part of the built-in namespace. Instead, exit is loaded automatically by the site module. Heres is the code with the function site.main that is doing it: https://github.com/python/cpython/blob/8af84b503d0b62a3db0d806d39f42c1e08746079/Lib/site.py#L634-L661 https://github.com/python/cpython/blob/8af84b503d0b62a3db0d8... and more specifically here https://github.com/python/cpython/blob/8af84b503d0b62a3db0d806d39f42c1e08746079/Lib/site.py#L415 https://github.com/python/cpython/blob/8af84b503d0b62a3db0d8... on setquit The line builtins.exit = _sitebuiltins.Quitter('exit', eof) shows that exit is set as a function. The Quitter class, which exit is an instance of, has a __call__ method, making it callable, so it as a function. I don't believe you're wrong not understanding it; it's just that the process isn’t typically explained in detail, especially what happens when you start the REPL. This is why the message "Use exit() instead..." exists in the REPL, because of the need for clarification. In a nutshell, exit is a function loaded into the built-ins by the site.py module, which automatically activates when the REPL starts. This automatic loading is what makes exit, help, __copyright__ and others available only in the interactive sessions.
- aeturnum 2y ago
  It seems great to change the REPL to treat it like a statement! This is obviously a better user experience. I also think it's somewhat funny given Python's history on "should common functionality be accessed through statements or functions"[1]! [1] I hope it's obvious that special-casing exit in the REPL is a much more constrained special case than print being a keyword and the difference in scope makes all the difference in balancing accessibility and consistency.

dmart 3y ago

There’s a sense in which it’s pedantically correct - ‘exit’ (and ‘help’) are not Python keywords outside of the REPL, so a beginner might try to use it in a script (maybe like sys.exit()?) and be confused. But I think the convenience is worth it.

mariocesar 2y ago
Yes, but it goes against the principles of "Explicit is better than implicit" and "There should be one-- and preferably only one—-obvious way to do it." We use parentheses () to call a function. print was a keyword in Python2, now, with print(), it's clear that we are calling for the execution. It's fun because `exit` alone in the REPL will return an object, and you can get the `exit.eof`, where is the message of what the keyword shortcut to call exit is, and it changes depending on the OS.

OutOfHere 3y ago

That's because `exit` will never work in a script, but `exit()` can.

mariocesar 3y ago
note that `exit()` on a script will also not work, as the exit function is only loaded on REPL. To make it work on a script, you will need to import the sys package and later call sys.exit()
- OutOfHere 2y ago
  `exit()` absolutely works in a script assuming that the `site` module was not bypassed at startup via `python -S`. I understand that `sys.exit()` and others are preferred.

mariocesar 3y ago

I think there's a bit of a misunderstanding regarding exit. exit is not a keyword or a REPL command, it's actually a function exposed in the builtin package. you can run "import builtins; builtins.exit()" and see that is there To clarify, there are two things here: why exit exists in the REPL, and why it's a function. The exit() function is available only in the REPL, and it appears built-in, but it isn't part of the built-in namespace. Instead, exit is loaded automatically by the site module. Heres is the code with the function site.main that is doing it: https://github.com/python/cpython/blob/8af84b503d0b62a3db0d806d39f42c1e08746079/Lib/site.py#L634-L661 https://github.com/python/cpython/blob/8af84b503d0b62a3db0d8... and more specifically here https://github.com/python/cpython/blob/8af84b503d0b62a3db0d806d39f42c1e08746079/Lib/site.py#L415 https://github.com/python/cpython/blob/8af84b503d0b62a3db0d8... on setquit The line builtins.exit = _sitebuiltins.Quitter('exit', eof) shows that exit is set as a function. The Quitter class, which exit is an instance of, has a __call__ method, making it callable, so it as a function. I don't believe you're wrong not understanding it; it's just that the process isn’t typically explained in detail, especially what happens when you start the REPL. This is why the message "Use exit() instead..." exists in the REPL, because of the need for clarification. In a nutshell, exit is a function loaded into the built-ins by the site.py module, which automatically activates when the REPL starts. This automatic loading is what makes exit, help, __copyright__ and others available only in the interactive sessions.

aeturnum 2y ago
It seems great to change the REPL to treat it like a statement! This is obviously a better user experience. I also think it's somewhat funny given Python's history on "should common functionality be accessed through statements or functions"[1]! [1] I hope it's obvious that special-casing exit in the REPL is a much more constrained special case than print being a keyword and the difference in scope makes all the difference in balancing accessibility and consistency.