Hello, a discussion began on python-dev about this. It began by a bug report, but is shifted and it now belongs to this discussion group.
The problem I find with augmented assignment is it's too complex, it's badly explained, it's error-prone. And most of all, I don't see any use-case for it ! The most common error is to consider that : a += b <==> a.__iadd__(b) when the truth is : a += b <==> a = a.__iadd__(b) which can be very confusing, as the two "a" are not necessarily the same. It then leads to subtle errors like: >>> class A(object): >>> a = 0 >>> a = A() >>> b = A() >>> a.a += 1 >>> A.a += 2 >>> print a.a 1 >>> print b.a 2 Also, the following behavior is pretty confusing : >>> a = [1] >>> b = [a] >>> c = (a,) >>> b[0] += [2] # Ok, no pb >>> print a [1,2] >>> c[0] += [3] Traceback (most recent call last): File "<string>", line 1, in ? TypeError: object doesn't support item assignment >>> print a [1,2,3] Then, in the standard library, there is no use-case of user-defined augmented assignment I could find. Of course, I find the augmented assignement itself very useful ! I use it a lot with immutable objects (strings, numbers, tuples, ...) but I tend to avoid it with mutables, and so it seems in the standard library that uses extensively the "extend" method of lists and very seldom the "+=" operator with lists. And even where the "a+=b" is used, it could be replaced with either "a.extend(b)" or "a = a+b" without bugs. So, what I would suggest is to drop the user-defined augmented assignment and to ensure this equivalence : a X= b <=> a = a X b with 'X' begin one of the operators. Pierre -- http://mail.python.org/mailman/listinfo/python-list
