Singly-Linked List

singly_linked_list.py

class Node:
    def __init__(self, key, next):
        self.key = key
        self.next = next

class List:
    def __init__(self, head=None):
        self.head = head
        self.tail = None
    
    def push_front(self, key):
        self.head = Node(key, self.head)
        if self.tail == None:
            self.tail = self.head
    
    def top_front(self):
        return self.head
    
    def pop_front(self):
        if head == None:
            raise KeyError
        self.head = self.head.next
        if self.head == None:
            self.tail == None
    
    def push_back(self, key):
        new_node = Node(key, None)
        if self.tail == None:
            self.tail = new_node
            self.head = self.tail
        else:
            self.tail.next = new_node
            self.tail = new_node
    
    def pop_back(self):
        if self.head == None:
            raise KeyError
        if self.head == self.tail:
            self.head = None
            self.tail = self.head
        else:
            p = self.head
            while p.next.next != None:
                p = p.next
            p.next = None
            self.tail = p  
    
    def find(self, key):
        pass
    
    def erase(self, key):
        pass
    
    def empty(self)
        pass
    
    def add_before(self, node, key):
        pass