The difference between these two cases are explained when also taking into consideration the initial PEP for extended unpacking:
PEP 3132 -- Extended iterable unpacking.
In the Abstract for that PEP we can see that:
This PEP proposes a change to iterable unpacking syntax, allowing to specify a “catch-all” name which will be assigned a list of all items not assigned to a “regular” name.
So in the first case, after executing:
*elements, = iterable
elements is always going to be a
list containing all the items in the
Even though it seems similar in both cases, the
* in this case (left-side) means: catch everything that isn’t assigned to a name and assign it to the starred expression. It works in a similar fashion as
**kwargs do in function definitions.
def spam(*args, **kwargs): """ args and kwargs group positional and keywords respectively """
The second case (right-side) is somewhat different. Here we don’t have the
* working in a “catch everything” way as much as we have it working as it usually does in function calls. It expands the contents of the iterable it is attached to. So, the statement:
elements = *iterable,
can be viewed as:
elements = 1, 2, 3, 4,
which is another way for a
tuple to be initialized.
Do note, a
list can be created by simple using
elements = [*iterable] which will unpack the contents of
 and result in an assignments of the form
elements = [1, 2, 3, 4].