On Wed, Apr 18, 2018 at 5:28 AM, Tim Peters <tim.pet...@gmail.com> wrote: > I'll channel that Guido would be happiest if this rule were followed: > > Given an assignment statement using "=", the meaning is the same if > "=" is replaced with ":=".
That's broadly the intention. At the moment, there are two exceptions: 1) Augmented assignment isn't a thing 2) Chained assignment isn't a thing, which means that the assignments operate right-to-left 2a) Assignment > In particular, the expression at the far right is evaluated once, and > - in case of chained assignments - is applied in turn to each target > left-to-right. I'll toy with this and see if I can implement it sanely. If so, that'll eliminate one more distinction. > Otherwise the semantics of "=" and ":=" can be very different indeed. TBH, the common cases won't actually be much affected. You give this example: k := container[k] := value but that's not going to be more common. What I'm more likely to see is something like this: k, container[k] = new_key(), new_value() which can instead be written: container[k := new_key()] = new_value() and is, IMO, clearer that way. > So, then, e.g., and assuming the rule above always applies: > > [Nick] >> Tuple unpacking: >> >> What's the result type for "a, b, c := range(3)"? Is it a range() >> object? Or is it a 3-tuple? If it's a 3-tuple, is that 3-tuple "(1, 2, >> 3)" or "(a, b, range(3))"? > > It's the range object range(3). Same as in: > > x = a, b, c = range(3) > > `x` is bound to the range object range(3). At the moment, "x = a, b, c := range(3)" will set c to range(3), then build a tuple of that with the existing values of a and b. You can, however, parenthesize the (a, b, c) part, and then it'll behave as you say. >> Whichever answers we chose would be surprising at least some of the >> time, so it seems simplest to disallow such ambiguous constructs, such >> that the only possible interpretation is as "(a, b, range(3))" > > That's why Guido would be happiest with the rule at the top. "The > answers" can already be surprising at times with current assignment > statements, but they are well defined. It would be mondo bonkers to > make up entirely different subtle answers ;-) Wholeheartedly agreed. 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
