LinkedNode and its use in Stack and Queue implementation, Python 3

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"""
LinkedNode class and its use in Stack and Queue implementation

Author: Jayesh Chandrapal
"""
class LinkedNode:
    __slots__ = "value", "link"
    
    def __init__(self, value, link = None):
        self.value = value
        self.link = link
        
    def __str__(self):
        return str(self.value)
    
    def __repr__(self):
        return "LinkedNode(" + repr(self.value) + "," + repr(self.link) + ")"
    
def testLinkedNode():
    nodes = LinkedNode(10, LinkedNode(20, LinkedNode(30)))
    
    n = nodes
    while n is not None:
        print(n.value)
        n = n.link
        
    print()
    print(nodes)
    print(repr(nodes))

# Stack implementation
class Stack:
    __slots__ = "top", "length"
    
    def __init__(self):
        self.top = None
        self.length = 0
        
    def __str__(self):
        current = top
        while current is not None:
            print(current.value)
            current = current.link
        
    def push(self, value):
        self.top = LinkedNode(value, self.top)
        self.length += 1
        
    def peek(self):
        return self.top.value
        
    def pop(self):
        temp = self.top.value
        self.top = self.top.link
        self.length -= 1
        return temp
        
    def empty(self):
        return self.top == None
        
    def size(self):
        return self.length

def testStack():
    stack = Stack()
    stack.push(10)
    assert stack.size() == 1
    stack.push(20)
    assert stack.size() == 2
    assert stack.peek() == 20
    assert stack.pop() == 20
    assert stack.size() == 1
    assert stack.pop() == 10
    assert stack.size() == 0
    print("all tests passed")
    
# Queue implementation
class Queue:
    __slots__ = "front", "back", "length"
    
    def __init__(self):
        self.front = None
        self.back = None
        self.length = 0
        
    def __str__(self):
        current = top
        while current is not None:
            print(current.value)
            current = current.link
        
    def enqueue(self, value):
        self.front = LinkedNode(value, self.top)
        self.length += 1
        
    def peek(self):
        return self.top.value
        
    def dequeue(self):
        temp = self.top.value
        self.top = self.top.link
        self.length -= 1
        return temp
        
    def empty(self):
        return self.front == None
        
    def size(self):
        return self.length

if __name__ == "__main__":
    #testLinkedNode()
    testStack()

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