$($Python$)$ Define a function named pop that removes the item at a given position from a singly linked structure. This function expects a position as a first argument, with the precondition $0<=$ position $<$ length of structure. Its second argument is the linked structure, which, of course, cannot be empty. The function returns a tuple containing the modified linked structure and the item that was removed. An example call is $($head$,$ item$)=$ pop$(1,$ head$).$

def pop$($index$,$ head$)$: