How to create a Fixed size Queue in Python
Borislav Hadzhiev
Last updated: Jun 16, 2022
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Create a Fixed size Queue in Python #
Use the deque class from the collections module to create a fixed size queue
in Python, e.g. deq = deque(maxlen=3). The class takes a maxlen argument
that determines the maximum length of the deque.
from collections import deque deq = deque(maxlen=3) deq.extend([1, 2, 3]) print(deq) # 👉️ deque([1, 2, 3], maxlen=3) deq.append(4) print(deq) # 👉️ deque([2, 3, 4], maxlen=3)
We used the
collections.deque
class to initialize a deque object.
You can also pass an iterable to the class to initialize the deque object with
items.
from collections import deque # 👇️ initialize deque with items deq = deque([1, 2, 3], maxlen=3) print(deq) # 👉️ deque([1, 2, 3], maxlen=3) deq.append(4) print(deq) # 👉️ deque([2, 3, 4], maxlen=3)
The deque class takes a maxlen argument. If the argument is not provided or
is None, the deque object can grow to an arbitrary length.
maxlen argument is provided and the deque is full, when new items are added, the same number of items are discarded from the opposite end.If we
append
a new item to the deque, an item from the start of the deque is discarded.
from collections import deque deq = deque([1, 2, 3], maxlen=3) print(deq) # 👉️ deque([1, 2, 3], maxlen=3) deq.append(4) print(deq) # 👉️ deque([2, 3, 4], maxlen=3)
Conversely, if we use the
appendleft
method to add an item to the left side of the deque, an item from the end of
the deque is discarded.
from collections import deque deq = deque([1, 2, 3], maxlen=3) print(deq) # 👉️ deque([1, 2, 3], maxlen=3) deq.appendleft(0) print(deq) # 👉️ deque([0, 1, 2], maxlen=3)
