Python Program to Implement Dequeue

This is a Python program to implement a dequeue.

Problem Description

The program creates a dequeue and allows the user to perform append and pop operations on it from both sides.

Problem Solution

1. Create a class Dequeue with instance variable items initialized to an empty list.
2. Define methods append, append_left, pop, pop_left and is_empty inside the class Dequeue.
3. The method append appends data to items from the right.
4. The method append_left appends data to items from the left.
5. The method pop pops from the right from items.
6. The method pop_left pops from the left from items.
7. The method is_empty returns True only if items is empty.

Program/Source Code

Here is the source code of a Python program to implement a dequeue. The program output is shown below.

class Dequeue:
    def __init__(self):
        self.items = []
 
    def is_empty(self):
        return self.items == []
 
    def append(self, data):
        self.items.append(data)
 
    def append_left(self, data):
        self.items.insert(0, data)
 
    def pop(self):
        return self.items.pop()
 
    def pop_left(self):
        return self.items.pop(0)
 
 
q = Dequeue()
print('Menu')
print('append <value>')
print('appendleft <value>')
print('pop')
print('popleft')
print('quit')
 
while True:
    do = input('What would you like to do? ').split()
 
    operation = do[0].strip().lower()
    if operation == 'append':
        q.append(int(do[1]))
    elif operation == 'appendleft':
        q.append_left(int(do[1]))
    elif operation == 'pop':
        if q.is_empty():
            print('Dequeue is empty.')
        else:
            print('Popped value from right: ', q.pop())
    elif operation == 'popleft':
        if q.is_empty():
            print('Dequeue is empty.')
        else:
            print('Popped value from left: ', q.pop_left())
    elif operation == 'quit':
        break
Program Explanation

1. An instance of Dequeue is created.
2. The user is presented with a menu to perform various operations on the dequeue.
3. The chosen operation is performed by calling the corresponding method of the dequeue.

advertisement
Runtime Test Cases
Case 1:
Menu
append <value>
appendleft <value>
pop
popleft
quit
What would you like to do? append 3
What would you like to do? append 4
What would you like to do? appendleft 2
What would you like to do? appendleft 1
What would you like to do? pop
Popped value from right:  4
What would you like to do? popleft
Popped value from left:  1
What would you like to do? pop
Popped value from right:  3
What would you like to do? popleft
Popped value from left:  2
What would you like to do? pop
Dequeue is empty.
What would you like to do? quit
 
Case 2:
Menu
append <value>
appendleft <value>
pop
popleft
quit
What would you like to do? append 1
What would you like to do? append 2
What would you like to do? pop
Popped value from right:  2
What would you like to do? pop
Popped value from right:  1
What would you like to do? appendleft 1
What would you like to do? appendleft 2
What would you like to do? pop
Popped value from right:  1
What would you like to do? pop
Popped value from right:  2
What would you like to do? append 1
What would you like to do? append 2
What would you like to do? popleft
Popped value from left:  1
What would you like to do? popleft
Popped value from left:  2
What would you like to do? quit

Sanfoundry Global Education & Learning Series – 1000 Python Programs.

If you wish to look at all Python Programming examples, go to 1000 Python Programs.

Free 30-Day Python Certification Bootcamp is Live. Join Now!

advertisement
advertisement
Subscribe to our Newsletters (Subject-wise). Participate in the Sanfoundry Certification contest to get free Certificate of Merit. Join our social networks below and stay updated with latest contests, videos, internships and jobs!

Youtube | Telegram | LinkedIn | Instagram | Facebook | Twitter | Pinterest
Manish Bhojasia - Founder & CTO at Sanfoundry
I’m Manish - Founder and CTO at Sanfoundry. I’ve been working in tech for over 25 years, with deep focus on Linux kernel, SAN technologies, Advanced C, Full Stack and Scalable website designs.

You can connect with me on LinkedIn, watch my Youtube Masterclasses, or join my Telegram tech discussions.

If you’re in your 40s–60s and exploring new directions in your career, I also offer mentoring. Learn more here.