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I'd have done both the hint and the actual result. Like this: >>> print <built-in function print> >>> exit <built-in function exit> Hint: U

I'd have done both the hint and the actual result. Like this: >>> print <built-in function print> >>> exit <built-in function exit> Hint: Use exit() or Ctrl-D (i.e. EOF) to exit >>> This way, it does do the thing you literally asked for, but also does help a newbie out.

ssgodderidge 3y ago
> does help a newbie out … or a long-time dev that switches languages fairly often :)
dmurray 3y ago
It should print the first to stdout and the second to stderr. That's completely consistent with how stdout and stderr are usually used. The regular Python REPL doesn't distinguish between stdout and stderr (perhaps it should!), but you can embed it in things like Jupyter notebooks that do.
- gruez 3y ago
  > It should print the first to stdout and the second to stderr. That's completely consistent with how stdout and stderr are usually used. That makes sense from a unix tool perspective, but not from a python repl perspective. The repl's behavior is to print the result from the last executed statement. For the exit function, the __repr__ method was overwriten to print the message. That way when you type in "exit", the last value would be exit (the function), and the overwritten __repr__ method causes the help message to be printed. There's no way to have it print to both without adding in some repl specific hacks. >>> exit Use exit() or Ctrl-Z plus Return to exit >>> exit.__repr__() 'Use exit() or Ctrl-Z plus Return to exit'
  - dmurray 3y ago
    How about def __repr__(self): import warnings warnings.warn("Use exit() or Ctrl-Z plus Return to exit") return super().repr()
    - edflsafoiewq 3y ago
      What if you aren't in the REPL? Using __repr__ at all seems like an abstraction violation. It should be the REPL's job to layer on special casing for exit.
      - dmurray 3y ago
        You could use the same pattern as DeprecationWarning. It's suppressed by default and test runners like pytest enable it. A new ReplWarning could be enabled by interactive tools only. I think I agree though: what you really want to special case is the situation where the user types precisely 'exit<cr>' at a REPL prompt, and that hack needs to exist further up the stack than in the implementation of __repr__.
      - amluto 3y ago
        The actual behavior is indeed a bit ridiculous: >>> print('%r' % str) <class 'str'> >>> def whatisit(x): ... print('It is %r' % x) ... >>> whatisit(min) It is <built-in function min> >>> whatisit(exit) It is Use exit() or Ctrl-D (i.e. EOF) to exit Excuse me? IMO if the REPL wanted a friendly feature like this, it should be a generic REPL feature, not a hack applied to the function exit.
        dale_glass 3y ago
        Also a bit funny: >>> def get_function(): ... return exit ... >>> a = get_function() >>> a Use exit() or Ctrl-D (i.e. EOF) to exit
  - hiccuphippo 3y ago
    Thanks for this, it never occurred to me it used __repr__ for the message. I just added this to my .pythonrc exit.__class__.__repr__ = lambda _: exit() quit = exit Edit, you also need this in your bashrc: export PYTHONSTARTUP=~/.pythonrc
IshKebab 3y ago
But really it should just exit. There's really no reason why it shouldn't. I think telnet does something stupid along the same lines "I know you want to quit but please ask address me as Sir first".
- AVincentInSpace 3y ago
  There would be two ways to implement that, neither of which are particularly good. You could either have the exit function call itself from its __repr__ method, which an abstraction violation so egregious it introduces security vulnerabilities (imagine a logger printing repr(thing) to stderr, and someone sneaking the exit function in there for it to print), or you could special case it by making exit a reserved word, which flies in the face of the Python 3 ethos which changed print from a reserved word to a function and breaks a lot of established code. Programming languages have rules that the programmer is expected to learn. Part of being a programmer is foregoing a certain amount of user friendliness in favor of an environment that is more powerful so that we can actually get things done. Programmers are paid to memorize and follow these rules so that the end user does not have to learn them.
  - IshKebab 3y ago
    You're trying to think of problems, not solutions. It's pretty easy to think of a good solution with few enough downsides that overall the design is much better: In the REPL only, if you type "exit" and press enter, it quits. No changes to Python semantics required. All code still works. Much friendlier UX. I wonder what dubious justification the Python Devs would come up with to avoid implementing that (and therefore admitting they've been wrong for 20 years). They'd probably try and claim it is more confusing to beginners or some nonsense like that.
bvisness 3y ago
Yes, I completely agree. If you want to teach the user the rules, then you follow the rules. The problem with the Python example is that they DID special-case it, but in an unhelpful way.
- thiht 3y ago
  How is it unhelpful? It literally tells what to do. Is it too hard to write exit() or press Ctrl+D after having incorrectly entered exit?
- Doxin 3y ago
  The special case is actually less a special case than you'd expect. It's "just" a python object that does some slightly funky things when turned into a string[0]. Making plain `exit` actually exit would mean triggering it accidentally could get too easy or would need a special case in the interpreter itself. [0] https://github.com/Source-Python-Dev-Team/Source.Python/blob/master/addons/source-python/Python3/_sitebuiltins.py#L13-L26 https://github.com/Source-Python-Dev-Team/Source.Python/blob...

ssgodderidge 3y ago

> does help a newbie out … or a long-time dev that switches languages fairly often :)

dmurray 3y ago

It should print the first to stdout and the second to stderr. That's completely consistent with how stdout and stderr are usually used. The regular Python REPL doesn't distinguish between stdout and stderr (perhaps it should!), but you can embed it in things like Jupyter notebooks that do.

gruez 3y ago
> It should print the first to stdout and the second to stderr. That's completely consistent with how stdout and stderr are usually used. That makes sense from a unix tool perspective, but not from a python repl perspective. The repl's behavior is to print the result from the last executed statement. For the exit function, the __repr__ method was overwriten to print the message. That way when you type in "exit", the last value would be exit (the function), and the overwritten __repr__ method causes the help message to be printed. There's no way to have it print to both without adding in some repl specific hacks. >>> exit Use exit() or Ctrl-Z plus Return to exit >>> exit.__repr__() 'Use exit() or Ctrl-Z plus Return to exit'
- dmurray 3y ago
  How about def __repr__(self): import warnings warnings.warn("Use exit() or Ctrl-Z plus Return to exit") return super().repr()
  - edflsafoiewq 3y ago
    What if you aren't in the REPL? Using __repr__ at all seems like an abstraction violation. It should be the REPL's job to layer on special casing for exit.
    - dmurray 3y ago
      You could use the same pattern as DeprecationWarning. It's suppressed by default and test runners like pytest enable it. A new ReplWarning could be enabled by interactive tools only. I think I agree though: what you really want to special case is the situation where the user types precisely 'exit<cr>' at a REPL prompt, and that hack needs to exist further up the stack than in the implementation of __repr__.
    - amluto 3y ago
      The actual behavior is indeed a bit ridiculous: >>> print('%r' % str) <class 'str'> >>> def whatisit(x): ... print('It is %r' % x) ... >>> whatisit(min) It is <built-in function min> >>> whatisit(exit) It is Use exit() or Ctrl-D (i.e. EOF) to exit Excuse me? IMO if the REPL wanted a friendly feature like this, it should be a generic REPL feature, not a hack applied to the function exit.
      - dale_glass 3y ago
        Also a bit funny: >>> def get_function(): ... return exit ... >>> a = get_function() >>> a Use exit() or Ctrl-D (i.e. EOF) to exit
- hiccuphippo 3y ago
  Thanks for this, it never occurred to me it used __repr__ for the message. I just added this to my .pythonrc exit.__class__.__repr__ = lambda _: exit() quit = exit Edit, you also need this in your bashrc: export PYTHONSTARTUP=~/.pythonrc

IshKebab 3y ago

But really it should just exit. There's really no reason why it shouldn't. I think telnet does something stupid along the same lines "I know you want to quit but please ask address me as Sir first".

AVincentInSpace 3y ago
There would be two ways to implement that, neither of which are particularly good. You could either have the exit function call itself from its __repr__ method, which an abstraction violation so egregious it introduces security vulnerabilities (imagine a logger printing repr(thing) to stderr, and someone sneaking the exit function in there for it to print), or you could special case it by making exit a reserved word, which flies in the face of the Python 3 ethos which changed print from a reserved word to a function and breaks a lot of established code. Programming languages have rules that the programmer is expected to learn. Part of being a programmer is foregoing a certain amount of user friendliness in favor of an environment that is more powerful so that we can actually get things done. Programmers are paid to memorize and follow these rules so that the end user does not have to learn them.
- IshKebab 3y ago
  You're trying to think of problems, not solutions. It's pretty easy to think of a good solution with few enough downsides that overall the design is much better: In the REPL only, if you type "exit" and press enter, it quits. No changes to Python semantics required. All code still works. Much friendlier UX. I wonder what dubious justification the Python Devs would come up with to avoid implementing that (and therefore admitting they've been wrong for 20 years). They'd probably try and claim it is more confusing to beginners or some nonsense like that.

bvisness 3y ago

Yes, I completely agree. If you want to teach the user the rules, then you follow the rules. The problem with the Python example is that they DID special-case it, but in an unhelpful way.

thiht 3y ago
How is it unhelpful? It literally tells what to do. Is it too hard to write exit() or press Ctrl+D after having incorrectly entered exit?
Doxin 3y ago
The special case is actually less a special case than you'd expect. It's "just" a python object that does some slightly funky things when turned into a string[0]. Making plain `exit` actually exit would mean triggering it accidentally could get too easy or would need a special case in the interpreter itself. [0] https://github.com/Source-Python-Dev-Team/Source.Python/blob/master/addons/source-python/Python3/_sitebuiltins.py#L13-L26 https://github.com/Source-Python-Dev-Team/Source.Python/blob...