maxlen holds an integer number that specifies the maximum length of the deque.Īs mentioned previously, if you don’t supply an iterable, then you get an empty deque.

iterable holds an iterable that provides the initialization data.

The deque initializer takes the following two optional arguments: The initialization goes from left to right using deque.append(). If you provide and input iterable, then deque initializes the new instance with data from it. If you instantiate deque without providing an iterable as an argument, then you get an empty deque. > from collections import deque > # Create an empty deque > deque () deque() > # Use different iterables to create deques > deque (( 1, 2, 3, 4 )) deque() > deque () deque() > deque ( range ( 1, 5 )) deque() > deque ( 'abcd' ) deque() > numbers = > deque ( numbers. You just need to import deque from collections and call it with an optional iterable as an argument:

Ensures fast, memory-efficient, and thread-safe pop and append operations on both endsĬreating deque instances is a straightforward process.

Supports built-in functions that operate on sequences and iterables, such as len(), sorted(), reversed(), and more.

Doesn’t support slicing, like in a_deque.

Supports membership operations with the in operator.Here’s a summary of the main characteristics of deque: If you do so, then once a deque is full, it automatically discards items from one end when you append new items on the opposite end. These features make deques particularly useful for creating custom stacks and queues in Python.ĭeques are also the way to go if you need to keep a list of last-seen items because you can restrict the maximum length of your deques. Additionally, append and pop operations on deques are also thread safe and memory efficient. Note: deque is pronounced as “deck.” The name stands for double- ended queue.Īppend and pop operations on both ends of a deque object are stable and equally efficient because deques are implemented as a doubly linked list. They support memory-efficient and fast append and pop operations on both ends of the data structure.

pop() in Python list.ĭeques are sequence-like data types designed as a generalization of stacks and queues. This data type was specially designed to overcome the efficiency problems of. Python’s deque was the first data type added to the collections module back in Python 2.4. However, the performance issues you saw before can significantly affect the overall performance of your applications. pop(), they’re usable as stacks and queues. Since Python lists provide both operations with. However, when Python needs to reallocate memory to grow the underlying list for accepting new items, these operations are slower and can become O( n).Īdditionally, appending and popping items on the left end of a Python list are known to be inefficient operations with O( n) speed. If you use the Big O notation for time complexity, then you can say that they’re O(1). Getting Started With Python’s dequeĪppending items to and popping them from the right end of a Python list are normally efficient operations. It’ll also be beneficial for you to have a general understanding of queues and stacks.įinally, you’ll write a few examples that walk you through some common use cases of deque, which is one of Python’s most powerful data types.įree Download: Get a sample chapter from Python Tricks: The Book that shows you Python’s best practices with simple examples you can apply instantly to write more beautiful + Pythonic code. To better understand these topics, you should know the basics of working with Python lists. When it’s worth using deque instead of list.How to use deque to build efficient queues and stacks.How to efficiently append and pop items from both ends of a deque.How to create and use Python’s deque in your code.Python’s deque is a low-level and highly optimized double-ended queue that’s useful for implementing elegant, efficient, and Pythonic queues and stacks, which are the most common list-like data types in computing. Python’s collections module provides a class called deque that’s specially designed to provide fast and memory-efficient ways to append and pop item from both ends of the underlying data structure. If you often work with lists in Python, then you probably know that they don’t perform fast enough when you need to pop and append items on their left end.

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