4️⃣

2.4 Stacks

What is a Stack?

A Stack is a linear data structure that saves data in Last In / First Out order. This is the exact opposite of a queue. It's the same as the undo function.

Simple Way to Make a Stack

Here we define a function called Stack and make a list inside called stack_list. Inside that list we add some values in this case 100, 200 and 300. After we print the value we start removing values from the end of the list which in this case we would remove 300 first, then 200, and lastly 100 until we return an empty list.
The biggest issue we face while implementing stacks is as the data grows so does its runtime. As the stack grows bigger, Python will have to do some memory work to make the data fit. This can lead to longer wait times for data to append.

Visualization:

def Stack(): # Make Stack List stack_list = [] # Appending Data To Stack List stack_list.append(100) stack_list.append(200) stack_list.append(300) print(stack_list) #Removes Last Item "Last In First Out" stack_list.pop() stack_list.pop() stack_list.pop() # Returns list return stack_list a = Stack() print(a)

Python Cleaner Implementation

Below is the same thing as above but it uses classes.
class Stack: def __init__(self): # Make List self.stack_list = [] def appending(self, item): # Checks to see if there are any duplicates in list if item in self.stack_list: #If so it returns error return "Value Already Exists" else: self.stack_list.append(item) def pops(self): # Checks to see if list is empty if len(self.stack_list) != 0: # if it isn’t empty it removes last value return self.stack_list.pop() else: return "List is Empty" Check_Stack = Stack() #Should add value to list Check_Stack.appending(100) Check_Stack.appending(200) Check_Stack.appending(300) #Should print 300 and then 200 print(Check_Stack.pops())
View code on GitHub.
 
⚖️
Copyright © 2021 Code 4 Tomorrow. All rights reserved. The code in this course is licensed under the MIT License. If you would like to use content from any of our courses, you must obtain our explicit written permission and provide credit. Please contact classes@code4tomorrow.org for inquiries.