Basic definition and usage examples of python stack [initialization, assignment, in-stack, out-stack, etc.].

# -*- coding:utf-8 -*-
#! python3
# In the design of a wharf, we need to define an instance of the attribute top. three instance methods: fetch the top element of the stack peek(); out pop(); in push()
The effect of #stacks: first in, last out
class Node(object):  ## node, including two attributes, a value for the node and the next pointing for the node
 def __init__(self,value):
   = value   # Assign a value to a node
   = None   # node's next pointing to
class stack(object):
 def __init__(self):
   = None    # Create a stack, give top the top-of-stack attribute, and top is initially empty.
 def peek(self):     # Get the element at the top of the stack and return the corresponding value.
  if != None:   # If the top of the stack is not empty, that is, there is data on the stack
   return  # Then just return to the top of the stack
  else:
   return None    # If there is no data on the stack, return None
 def push(self,node):    # Add elements to the stack (arguments include self and node's value, node)
  if node != None:    # If the node, which is joined, is not empty
   packNode = Node(node)  # Instantiate the Node class
    =  # Assign the pointing of the added node to the top of the stack
    = packNode   # Assign the node at the top of the stack to the added node
   return   # Return the value of the node
  else:
   return None    # Returns None
 def pop(self):     # Out of the stack
  if  == None:  # If the stack is empty
   return None    # Returns None
  else:
   tmp =   # Pass the top-of-stack value to tmp
    =  # Change the stack top pointing to the next node on the current stack top
   return tmp     # Returns the value of the node that went out of the stack
s = stack()
a = Node(1)
print((a).value)
print((2))
print((3))
print(())
print((4))
print(())
print(())
print(())
print(().value)