Python – Get the Max Size of a Deque

In this tutorial, we will look at how to get the max size of a deque in Python with the help of some examples.

deque in Python

The collections module in Python comes with a deque class that you can use to implement a stack or queue data structure in Python. Deques support thread-safe, memory efficient appends and pops from either side of the deque with approximately the same O(1) performance in either direction.

In simple terms, you can think of a deque in Python as a list-like data structure but with efficient insertion and removal of items from either end (left and right). This makes them very useful when implementing a stack or queue functionality in Python.

How to get the max size of a deque in Python?

The deque class comes with a number of built-in functions to help perform common operations (like adding and removing elements).

The max size of a deque is defined only for bounded deques (deques with a size limit). To get the max size of a deque in Python, use the deque maxlen attribute. The following is the syntax –

# get the max size of deque
queue.maxlen

The maxlen attribute of a deque is set during its creation. By default, it’s set to None (which indicates an unbounded deque) unless specified otherwise (in which case, the deque will be a bounded deque).

Examples

Let’s now look at some examples of using the above syntax –

Example 1 – Max size of an unbounded deque

First, let’s create an unbounded deque (deque without a set maxlen) with some elements.

from collections import deque

# create a deque
queue = deque([1, 2, 3])
# print the deque
print(queue)

Output:

deque([1, 2, 3])

Here, we imported the deque class from the collections module and created a deque object, queue with three elements – 1, 2, and 3.

Now, let’s now get its max size using its maxlen attribute.

# get the max size of deque
print(queue.maxlen)

Output:

None

We get the max size of deque as None because the deque under consideration is an unbounded deque. The value of the maxlen attribute is None for unbounded deques.

Example 2 – Max size of a bounded deque

Let’s now create a bounded deque (deque object with a specified maxlen which defines the maximum number of values that it can store).

# create a bounded deque
queue = deque([1, 2, 3], maxlen=4)
# print the deque
print(queue)

Output:

deque([1, 2, 3], maxlen=4)

Here, we created a bounded deque with maxlen 4 and three elements inside it. Now, let’s get its max size using its maxlen attribute.

# get the max size of deque
print(queue.maxlen)

Output:

4

We get the deque’s max size as 4.

Length vs the max length of a deque

It’s important to not confuse the maxlen (the max size) of deque with its length (which you can get using the Python built-in len() function.

The length of a deque is the number of elements in a deque. Both bounded and unbounded deques have a length. The maxlen (the max size) of a deque, on the other hand, is defined only for bounded deques and represents the maximum number of values the deque can have.

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