On Sep 28, 2005, at 9:12 AM, Reinhold Birkenfeld wrote:
Hi,
a general question. Consider:
class A(list): def __setitem__(self, index, item): # do something with index and item return list.__setitem__(self, index, item)
lst = A([1,set()])
lst[0] |= 1
lst[1] |= set([1])
Do we want lst.__setitem__ to be called in the second inplace assignment?
Yes. Right now, you can roughly explain the behavior by stating that, after "x=a", "x |= y" is the same as "x = x | y", except that "a"'s value is undefined (it might have changed, or it might have not).
A case where this matters is here: http://python.org/sf/1306777
This confusion between modification of immutable types and modification of mutable types is why I feel that it's often best to simply avoid the inplace operators in favor of their explicit equivalents. In this case, set.update(). James