After 30 years am I not allowed to take new information into account and consider a change of heart? :-)
On Mon, Apr 6, 2020 at 6:21 PM Steven D'Aprano <st...@pearwood.info> wrote: > On Mon, Apr 06, 2020 at 11:54:54AM -0700, Guido van Rossum wrote: > > > (In an early version of the PEG parser, all keywords were > > context-sensitive, and there were only very few places in the grammar > where > > this required us to insert negative lookaheads to make edge cases parse > > correctly. The rest was taken care by careful ordering of rules, e.g. the > > rule for `del_stmt` must be tried before the rule for `expression_stmt` > > since `del *x` would match the latter.) > > I think, on first glance, I'd rather have all keywords context-sensitive > than just some. But I haven't put a great deal of thought into that > aspect of it, and I reserve the right to change my mind :-) > > > > > Personally, I would not like to have to explain to newcomers why > `match` > > > is a keyword but you can still use it as a function or variable, but > not > > > other keywords like `raise`, `in`, `def` etc. > > > > > > match expression: > > > match = True > > > > > > > What kind of newcomers do you have that they even notice that, unless you > > were to draw attention to it? > > It didn't take me 25 years to try using "of" and "if" for "output file" > and "input file", so I guess my answer to your question is ordinary > newcomers :-) > > "Newcomers" doesn't just including beginners to programming, it can > include people experienced in one or more other language coming to > Python for the first time. > > But if we're talking about complete beginners, the concept of what is > and isn't a keyword is not always clear. Why is the first of these legal > but not the second? Both words are highlighted in my editor: > > str = "Hello world" > class = "wizard" > > People are going to learn that `match` is a keyword, and then they are > going to come across code using it as a variable or method, and while > the context-sensitive rule might be obvious to us, it won't be obvious > to them precisely because they are still learning the language rules. > > I think that `match` would be an especially interesting case because I > can easily see someone starting off with a variable `match`, that they > handle in an `if` statement, and then as the code evolves they shift it > to a `match` statement: > > match match: > > and not bother to refactor the name because they are familiar enough > with is that the meaning is obvious. > > On the other hand there are definitely a few keywords that collide with > useful names. Apart from `if`, I have wanted to use these as variables, > parameters or functions: > > class, raise, in, from, except, while, lambda > > (off the top of my head, there may be others). There's at least one > place in the random module where a parameter is misspelled "lambd" > because lambda is a keyword. So there is certainly something to be said > for getting rid of keywords. > > On the third hand, keywords don't just make it easier for the > interpreter, they also make it easier for the human reader. You don't > need to care about context, `except` is `except` wherever you see it. > That makes it a dead-simple rule for anyone to learn, because there are > no exceptions, pun intended. > > (I guess inside strings and comments are exceptions, but they are > well-understood and *simple* exceptions.) > > I just can't help feeling at this point that while there are pros and > cons to making things a keyword, having some keywords be context > sensitive but not others is going to combine the worst of both and end > up be confusing and awkward. > > > > I'm serious -- from the kind of questions > > I've seen in user forums, most newcomers are having a hard enough time > > learning more fundamental concepts and abstractions than the precise > rules > > for reserved words. > > That's because the precise rules for reserved words are dead-simple to > learn. You can't use them anywhere except in the correct context. If we > start adding exceptions to that, that reserved words are only sometimes > reserved, I think that will make them harder to learn. If it's only some > reserved words but not others, that's even harder because we have three > classes of words: > > * words that are never reserved > * words that are sometimes reserved, depending on what is around them > * words that are always reserved > > I had thought that "no context-sensitive keywords" was a hard rule, so I > was surprised that you are now re-considering it. > > > -- > Steven > _______________________________________________ > Python-Dev mailing list -- python-dev@python.org > To unsubscribe send an email to python-dev-le...@python.org > https://mail.python.org/mailman3/lists/python-dev.python.org/ > Message archived at > https://mail.python.org/archives/list/python-dev@python.org/message/NNMJB7QIRAMROQU5XRM6YV7K4NXBGXBT/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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