A deque (short for “double-ended queue”) is a data structure from the collections module in Python that allows you to add and remove elements from both ends efficiently. It is a versatile and high-performance alternative to lists for certain use cases, especially when you need fast appends and pops from both ends of the queue.
1. Importing deque
To use deque, you first need to import it from the collections module:
from collections import deque
2. Creating a Deque
You can create a deque by passing an iterable (e.g., a list) to the deque constructor:
# Creating an empty deque
dq = deque()
# Creating a deque with initial elements
dq = deque([1, 2, 3, 4, 5])
3. Adding and Removing Elements
deque supports efficient appends and pops from both ends of the queue.
3.1 Appending Elements
# Appending elements to the right
dq.append(6)
# Appending elements to the left
dq.appendleft(0)
3.2 Removing Elements
# Removing elements from the right
dq.pop()
# Removing elements from the left
dq.popleft()
3.3 Example
from collections import deque
# Create a deque with initial elements
dq = deque([1, 2, 3])
# Append elements
dq.append(4) # deque([1, 2, 3, 4])
dq.appendleft(0) # deque([0, 1, 2, 3, 4])
# Remove elements
dq.pop() # deque([0, 1, 2, 3])
dq.popleft() # deque([1, 2, 3])
4. Rotating the Deque
deque also provides a method to rotate the elements. Positive values rotate the deque to the right, while negative values rotate it to the left:
# Rotating right by 2 steps
dq.rotate(2)
# Rotating left by 3 steps
dq.rotate(-3)
5. Accessing Elements
You can access elements in a deque using indexing, just like with a list:
# Accessing elements
element = dq[0] # First element
last_element = dq[-1] # Last element
6. Using Deque as a Queue
The deque is ideal for implementing queues where you need to efficiently add and remove elements from both ends:
from collections import deque
# Initialize deque
queue = deque()
# Enqueue (append) elements
queue.append('A')
queue.append('B')
# Dequeue (pop) elements
item = queue.popleft() # 'A'
7. Summary
The deque from the collections module is a flexible and efficient data structure for adding and removing elements from both ends. It supports operations like appending, popping, and rotating, making it a powerful tool for various applications where such operations are frequent.
