In this tutorial, we will look at how to check whether a deque in Python is empty or not 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 check if a deque is empty?

Deques in Python are collection-type objects. Similar to other collection types in Python such as lists, tuples, etc. you can check whether a deque object is empty or not by using it in a boolean context.
The following is the syntax –
# check if deque "queue" is empty not queue
Using a deque object in a boolean context will give True
if the deque is not empty and False
if the deque is empty. Since we directly want to check whether the deque is empty or not, we usenot queue
.
Alternatively, you can check if a deque is empty or not by checking if its length is equal to 0.
The following is the syntax –
# check if deque "queue" is empty len(queue)==0:
Examples
Let’s now look at some examples of using the above syntax
Example 1 – Check if a deque is empty in Python
First, let’s create two deques, one empty and the other non-empty (containing some elements).
from collections import deque # create an empty deque q1 = deque() # create a non-empty deque q2 = deque([1, 2, 3]) # print the deques print(q1) print(q2)
Output:
deque([]) deque([1, 2, 3])
Here, we imported the deque
class from the collections
module and created two deque objects – q1
, an empty deque, and q2
a deque with some values.
Let’s now check if the above-created deque objects are empty or not by using them in a boolean context.
# check if deque is empty print(not q1) print(not q2)
Output:
True False
We get True
for q1
(indicating that it’s empty) and False
for q2
(indicating that it’s not empty).
You can also check if a deque is empty or not by comparing its length to 0.
# check if deque is empty print(len(q1)==0) print(len(q2)==0)
Output:
True False
We get the same result as above.
Example 2 – Check if a bounded deque is empty
You can use the above methods to check if a deque is empty or not for bounded deques (deques with a specified maximum size) as well.
Let’s create two bounded deques, one empty and the other non-empty.
# create an empty bounded deque q1 = deque(maxlen=4) # create a non-empty deque q2 = deque([1, 2, 3], maxlen=4) # print the deques print(q1) print(q2)
Output:
deque([], maxlen=4) deque([1, 2, 3], maxlen=4)
Here, we created two bounded deques – q1
, an empty deque, and q2
a deque with some values.
Let’s now use check if these deques are empty or not by using them in a boolean context.
# check if deque is empty print(not q1) print(not q2)
Output:
True False
We get True
for q1
(indicating that it’s empty) and False
for q2
(indicating that it’s not empty).
We can also similarly use the len()
function to get their respective lengths and compare them with 0 to check whether the deques are empty or not.
# check if deque is empty print(len(q1)==0) print(len(q2)==0)
Output:
True False
We get the same result as above.
You might also be interested in –
- Python – Convert a deque of strings to a single string
- Python – Convert a deque to a list
- Python – Get the Index of the Maximum Value in Deque
- Python – Get the Index of the Minimum Value in Deque
- Python – Get the Maximum and the Minimum Value in a Deque
- Python – Get Value by Index in Deque
- Python – Count occurrences of a value in deque
- Python – Create a deque copy
- Python – Rotate a Deque to the Right and Left
- Python – Extend deque to the left
- Python – Extend deque to the right
- Python – Get the Max Size of a Deque
- Python – Reverse a deque
- Python – Get Index of a Value in Deque
- Python – Remove Element by Value in Deque
- Python – Remove all elements from a deque (clear deque)
- Python – Append Element to a Deque
- Python – Append Element to the Left in Deque
- Python – Pop Element From Left in Deque
- Python – Pop Element From the End in Deque
- Python – Insert Element at a given Index in Deque
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