def reverse(llist):
    curr_node = llist
    head = None
    while curr_node is not None:
        pre_node = curr_node.next
        curr_node.next = head
        head = curr_node
        curr_node = pre_node
    return head
    # Example process:
    # Initial list: head = (1) -> 2 -> 3 -> None
    # Reversed list building process:
    #
    # Before Loop:             head = (None),                curr_node = 1
    # While-loop:
    # Loop-1: pre_node = 2,    head = (1) -> None,           curr_node: 1 => 2
    # Loop-2: pre_node = 3,    head = (2) -> 1 -> None,      curr_node: 2 => 3
    # Loop-3: pre_node = None, head = (3) -> 2 -> 1 -> None, curr_node: 3 => None
    #
    # Reversed list: head = (3) -> 2 -> 1 -> None