4 ms·

> When I was in the Python interpreter and entered “exit”, which doesn’t work because exit is not a keyword, I got a message that told me how to actually exit.

by easton 5y ago

> When I was in the Python interpreter and entered “exit”, which doesn’t work because exit is not a keyword, I got a message that told me how to actually exit. This was something that one of those "Zen of Ruby" style articles brought up as a negative and although I'm not a Ruby person, I tend to agree. exit is not a keyword, but it is reserved so that you can get this message. Nobody can (or at least should) name a symbol exit, and alternative Python interpreters just turn "exit" into exit(). So why can't the normal interpreter do what I meant instead of being pedantic? It is generally user friendly in other cases (the new error messages in 3.10, for instance).

deleted 5y ago
[deleted]
nerdponx 5y ago
Because the built-in console doesn't support any special keywords or syntax. Other consoles already support special keywords and syntax, so it's no problem to interpret "exit" as one of those.
codeflo 5y ago
The context is good error messages; what you’re saying is that DWYM (do what you mean) is even better than a good error message. That’s sometimes true and can help beginners. But it also means more special cases and magic, which can make a language hard to learn in a different way. Python and Ruby are almost at the opposite ends of that trade-off, so it shouldn’t be surprising that a Ruby person doesn’t like Python’s solution. Also, and this is really off-topic, I also completely disagree that the names of built-in functions are off limits in a program, or should effectively be keywords. I'm not saying it's particularly wise to name a variable "print" or something. But should I learn by heart the names of all built in functions before naming any variable? Should I refactor my program whenever a new one is added? Resolving those kinds of conflicts is what scoping is for, and it works.
- Volundr 5y ago
  > The context is good error messages; what you’re saying is that DWYM (do what you mean) is even better than a good error message. I'm not sure that's true. "Just do what I mean" is an understandable response when you get an error message that hints that the program knew exactly what you meant. It feels like a human responding to "Can I have some water?" with "I don't know CAN you?", but it ignores the fact that the program doesn't really know what the user meant. Sure whoever authored the Python interpreter guessed that 99% of the time if you type `exit` you want to leave, but if they just assume that, then what happens if I'm actually trying to see what's in a variable `ext` (short for extension) and my fingers just auto completed `exit` because it's something I type so frequently (this kind of typo happens to me all the time). Suddenly the interpreter is dead and I have to start over on whatever I was doing. I'd actually rather the program gives me instruction on how to what it thinks I want to do, and let me decide if it's really what I mean.
luhn 5y ago
> exit is not a keyword, but it is reserved so that you can get this message. `exit` is not reserved. It's a callable implemented in pure Python [1] injected into the local scope when in interactive mode. There's no special functionality associated with it—The error message is implemented using the standard `__repr__` behavior. You are free to override the value of `exit` if you so choose. "Special cases aren't special enough to break the rules." [1] https://github.com/python/cpython/blob/06b8f1615b09099fae5c5393334b8716a4144d20/Lib/_sitebuiltins.py#L13 https://github.com/python/cpython/blob/06b8f1615b09099fae5c5...
- easton 5y ago
  Learn something new every day. I hadn't thought to check, just figured it was reserved since iPython used it fine. Thanks for the correction.

by easton 5y ago

deleted 5y ago

[deleted]

nerdponx 5y ago

Because the built-in console doesn't support any special keywords or syntax. Other consoles already support special keywords and syntax, so it's no problem to interpret "exit" as one of those.

codeflo 5y ago

The context is good error messages; what you’re saying is that DWYM (do what you mean) is even better than a good error message. That’s sometimes true and can help beginners. But it also means more special cases and magic, which can make a language hard to learn in a different way. Python and Ruby are almost at the opposite ends of that trade-off, so it shouldn’t be surprising that a Ruby person doesn’t like Python’s solution. Also, and this is really off-topic, I also completely disagree that the names of built-in functions are off limits in a program, or should effectively be keywords. I'm not saying it's particularly wise to name a variable "print" or something. But should I learn by heart the names of all built in functions before naming any variable? Should I refactor my program whenever a new one is added? Resolving those kinds of conflicts is what scoping is for, and it works.

Volundr 5y ago
> The context is good error messages; what you’re saying is that DWYM (do what you mean) is even better than a good error message. I'm not sure that's true. "Just do what I mean" is an understandable response when you get an error message that hints that the program knew exactly what you meant. It feels like a human responding to "Can I have some water?" with "I don't know CAN you?", but it ignores the fact that the program doesn't really know what the user meant. Sure whoever authored the Python interpreter guessed that 99% of the time if you type `exit` you want to leave, but if they just assume that, then what happens if I'm actually trying to see what's in a variable `ext` (short for extension) and my fingers just auto completed `exit` because it's something I type so frequently (this kind of typo happens to me all the time). Suddenly the interpreter is dead and I have to start over on whatever I was doing. I'd actually rather the program gives me instruction on how to what it thinks I want to do, and let me decide if it's really what I mean.

luhn 5y ago

> exit is not a keyword, but it is reserved so that you can get this message. `exit` is not reserved. It's a callable implemented in pure Python [1] injected into the local scope when in interactive mode. There's no special functionality associated with it—The error message is implemented using the standard `__repr__` behavior. You are free to override the value of `exit` if you so choose. "Special cases aren't special enough to break the rules." [1] https://github.com/python/cpython/blob/06b8f1615b09099fae5c5393334b8716a4144d20/Lib/_sitebuiltins.py#L13 https://github.com/python/cpython/blob/06b8f1615b09099fae5c5...

easton 5y ago
Learn something new every day. I hadn't thought to check, just figured it was reserved since iPython used it fine. Thanks for the correction.