Source: 📖 Effective Python item 13
Catch-all unpacking is a more advanced application of multiple assignment unpacking. A shortcoming of multiple assignment unpacking is that the left and right side of the = assignment operator must contain the same amount of items, as each item on the right goes into one variable on the left. This applies whether the items on the right are discreet values or the contents of a list.
my_list = [1, 2, 3, 4, 5, 6]
one, two = my_list # Raises ValueError
>>>
Traceback ...
ValueError: too many values to unpack (expected 2)
By using a starred variable with the syntax *varaible_name, all excess values can be unpacked into this container—this is catch-all unpacking. Starred expressions are always turned into a list object.
my_list = [1, 2, 3, 4, 5, 6]
one, two, *others = my_list
print(one)
print(two)
print(others)
>>>
1
2
[3, 4, 5, 6]
A starred variable can appear in any position, not just at the end:
my_list = [1, 2, 3, 4, 5, 6]
first, *others, last = my_list
print(first)
print(others)
print(last)
>>>
1
[2, 3, 4, 5]
6
my_list = [1, 2, 3, 4, 5, 6]
*others, second_last, last = my_list
print(others)
print(second_last)
print(last)
>>>
[1, 2, 3, 4]
5
6
The only caveats are that starred expressions must be used in combination with at least one other discreet expressions when unpacking, and multiple catch-all expressions cant be used together.