Sentinels and removal in Python

Questions 1 to 5 of 8

1. 1. The remove_careless function below raises an AttributeError when it is called on the first node of a plain doubly linked list. Why? ``python def remove_careless(node): node.prev.next = node.next node.next.prev = node.prev ``

   node.next is always None for the first nodeThe function needs a size argument that it does not receivenode.prev is None, so node.prev.next = ... sets an attribute on NoneA plain function cannot change the fields of a Node
2. 2. Using the CircularList class from this lesson, what does this code print? ``python lst = CircularList() lst.add_last(3) lst.add_first(1) lst.add_last(5) node = lst.find(5) lst.remove(node) lst.add_first(5) print(f"{lst} size={lst.size}") ``

   [1 <-> 3 <-> 5] size=3[5 <-> 1 <-> 3] size=3[5 <-> 1 <-> 3] size=4[3 <-> 1 <-> 5] size=3
3. 3. This loop should print every real value in a CircularList. What is wrong with it? ``python cur = lst.sentinel.next while cur is not None: print(cur.value) cur = cur.next ``

   It skips the first real node, because it starts at sentinel.nextIt prints the sentinel's value once and then stopsIt raises a SyntaxError, because cur.value is not a valid attributeThe test should be cur is not lst.sentinel. No link in the ring is None, so the loop goes around the ring and never stops
4. 4. Python has no final keyword for attributes. So the rule that self.sentinel is set once in __init__ and never assigned again is kept by ____ . Fill in the blank.

   Type your answer.

5. 5. Using the CircularList class from this lesson, which state is an empty list in, right after CircularList() runs?

   sentinel.next and sentinel.prev are both Nonesentinel.next points at the sentinel, but sentinel.prev is Nonesentinel.next and sentinel.prev both point at the sentinel itselfThe sentinel attribute is None, and size is 1