The
*b syntax is called extended iterable unpacking. It grabs everything in the middle of the list, leaving the first item (a) and the last (c) outside the star. This pattern is super handy, but can also behave unexpectedly if you assume it’ll grab just one item or not consider the structure of the data.The starred variable always gets a list, and it can be empty so plan accordingly when unpacking, especially in function arguments or loops.
For example: Consider the following code
x, *y = [42]
print(y) # []
No error, but
y is just an empty list! Unpacking doesn’t always fill every name the way you might guess.
