On Mon, Dec 28, 2020 at 09:06:40AM -0000, Anton Abrosimov wrote:
> Steven D'Aprano wrote:
> > You contradict yourself:
> > "I can implement any behaviour"
> > "I can't realize any other behaviour ..."
> > Which is correct?
>
> I apologize for my english, I meant that I cannot implement the
> following behavior inside the class:
>
> ```
> class MyClass:
> def __iter__(self):
> return self.items_for_iteration
> def __unpack__(self):
> return self.items_for_unpack
> ```
> I have to make a separate method and have to rely on the user of the class.
Ah, now I understand what you mean: you want iteration and iterator
unpacking to do different things:
obj = MyClass()
list(obj) # iteration
# --> returns a b c d
print(*obj) # iterator unpacking
# --> returns x y z
You can't do that, just like you can't make these different:
items = list(obj) # iteration
items = [item for item in obj] # iteration in a comprehension
items = []
for item in obj: # iteration in a for-loop
items.append(item)
And that is a **good thing** because it would be confusing and horrible
if iteration over an object was different depending on how you iterate
over it.
We're not going to invent new dunder methods:
def __iter__(self):
def __forloop__(self):
def __comprehension__(self):
so that they can be different, and I don't think we should invent a new
dunder method `__unpack__` so it can be different from iteration.
Iterator unpacking is just a form of iteration.
--
Steve
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