Stack In Python

Stack

A stack is a linear/sequential data structure in which insertion and deletion can take place at one end i.e. stack top. Stack is LIFO data structure i.e. Last In First Out

Operation that can be performed on stack are:
• PUSH: When a new element/item is added to the top of the stack, its called PUSH
• POP: When a new element/item is removed from the top of the stack, its called POP
• TRAVERSAL: Display the complete stack items

Implementation of stack using LIST:

In [1]:

#Creating a STACK
stack=list()
stack=[]

In [3]:

#Adding Element to the STACK
list.append()

In [ ]:

#Deleting an item from STACK
list.pop()
list.pop([i])

In [ ]:

# Program to implement a stack with LIST
stack=[]
c='y'
while (c=='y'):
    print("1. PUSH")
    print("2. POP")
    print("3. Display")
    choice=int(input("Enter your choices: "))
    if (choice==1):
        a=input("Enter any number: ")
        stack.append(a)
    elif (choice==2):
        if (stack==[]):
            print("Stack Empty")
        else:
            print("Deleted element is :", stack.pop())
    elif (choice==3):
        l=len(stack)
        for i in range(l-1,-1,-1):
            print(stack[i])
    else:
        print("wrong input")
    c=input("Do you want to continue or not? ")

1. PUSH
2. POP
3. Display
Enter your choices: 1
Enter any number: 15
Do you want to continue or not? y
1. PUSH
2. POP
3. Display
Enter your choices: 1
Enter any number: 36
Do you want to continue or not? y
1. PUSH
2. POP
3. Display
Enter your choices: 3
36
15

Application of Stacks:

• The copy,paste function is implemented using stack
• The redo, undo is implemented using stack
• Stack are used to avoid the use of operator precedence in multioperator operation expression evaluation
• The compilers use stack to store the previous state of a program wehn a function is called or during recursion

Assignment:

1. Write a program to display unique vowels present in the given word using stack
2. Write a program to add, delete and display the records of an employee using list using stack

CBSE Question:

1. Write a function in Python PUSH(Arr), where Arr is a list of numbers. From this list push all numbers divisible by 5 into a stack implemented by using a list. Display the stack if it has at least one element, otherwise display appropriate error message.

In [4]:

def push(arr):
    stack=[]
    for i in arr:
        if i%5==0:
          stack.append(i)  
    if stack==[]:
        print("The stack is empty")
    else:
        for i in range(len(stack)-1,-1,-1):
            print(stack[i])
            
push([15,47,48,9,5,12,10])

10
5
15

In [ ]: