On Wed, Apr 25, 2018 at 7:29 AM, Anthony Flury via Python-Dev <python-dev@python.org> wrote: > On 24/04/18 17:11, Yury Selivanov wrote: >> >> On Tue, Apr 24, 2018 at 12:03 PM, Ethan Furman <et...@stoneleaf.us> wrote: >> [..] >>> >>> But I do write this: >>> >>> def wrapper(func, some_value): >>> value_I_want = process(some_value) >>> def wrapped(*args, **kwds): >>> if value_I_want == 42: >>> ... >> >> But this pattern is more rare than comparing local variables. That's >> the point I'm trying to use. Besides, to make it an assignment >> expression under my proposal you would need to use parens. Which makes >> it even less likely that you confuse '=' and '=='. > > > Just because you wrap a set of character in parens doesn't mean that you > wont potentially mistype what you should type inside the parens. The failure > mode of in C : > > if (a = 3) > do_something_with_a(a); > > Is Incredibly common even with very experienced developers - so much so that > most linters flag it as a likely error, and I think gcc has an option to > flag it as a warning - even though it is valid and very occasionally it is > useful.
Technically what you have there trips *two* dodgy conditions, and could produce either warning or both: 1) Potential assignment where you meant comparison 2) Condition is always true. The combination makes it extremely likely that this wasn't intended. It's more dangerous, though, when the RHS is a function call... > Also many developers who come to Python from languages such as C will still > place parens around conditionals - this means that a typo which will cause a > Syntax Error in current versions, but would cause a potentially subtle bug > under your implementation (unless you maintain the rule that you can't > rebind currently bound names - which renders the whole idea useless in loops > (as already discussed at length). Yuri, look how many of the python-dev readers have completely misinterpreted this "can't rebind" rule. I think that's a fairly clear indication that the rule is not going to be well understood by anyone who isn't extremely familiar with the way the language is parsed. I hesitate to say outright that it is a *bad rule*, but that's the lines I'm thinking along. ChrisA _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
