On Thu, Jul 3, 2014 at 5:51 PM, candide <c.cand...@laposte.net> wrote: > Good and interesting observation. But I can't find out where this feature is > referenced in the Language/Library Reference. Because, as my first post > explains, augmented assignment performs the binary operation associated to > the augmented assignment, cf. > > https://docs.python.org/3.2/reference/simple_stmts.html#augmented-assignment-statements > > so seq+= {5, 6} performs seq + {5, 6}, the later raising a TypeError.
>From that link: """ An augmented assignment expression like x += 1 can be rewritten as x = x + 1 to achieve a similar, but not exactly equal effect. In the augmented version, x is only evaluated once. Also, when possible, the actual operation is performed in-place, meaning that rather than creating a new object and assigning that to the target, the old object is modified instead. """ The significance here is that the augmented assignment may not necessarily be at all comparable to the non-augmented version, but ought to have *approximately* the same *intention*. There are plenty of situations where the two will differ, eg when there are multiple references to the same object: >>> a = b = [1,2] >>> a += [3] >>> a,b ([1, 2, 3], [1, 2, 3]) >>> a = a + [4] >>> a,b ([1, 2, 3, 4], [1, 2, 3]) In its simplest form, x += 1 <-> x = x + 1, but there are plenty of ways to distinguish them. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
