TheAlgorithms/Python · error · OverflowError

Maximum queue size is 100

Error message

Maximum queue size is 100

What it means

Raised by FixedPriorityQueue.enqueue() (data_structures/queues/priority_queue_using_list.py:84) when the target priority bucket (a plain Python list) already holds 100 elements. Each of the three priority levels is hard-capped at 100 items in this demo implementation. Note this is the builtin OverflowError, raised inside a try that only catches IndexError, so it propagates untouched.

Source

Thrown at data_structures/queues/priority_queue_using_list.py:84

    Priority 2: []
    """  # noqa: E501

    def __init__(self):
        self.queues = [
            [],
            [],
            [],
        ]

    def enqueue(self, priority: int, data: int) -> None:
        """
        Add an element to a queue based on its priority.
        If the priority is invalid ValueError is raised.
        If the queue is full an OverFlowError is raised.
        """
        try:
            if len(self.queues[priority]) >= 100:
                raise OverflowError("Maximum queue size is 100")
            self.queues[priority].append(data)
        except IndexError:
            raise ValueError("Valid priorities are 0, 1, and 2")

    def dequeue(self) -> int:
        """
        Return the highest priority element in FIFO order.
        If the queue is empty then an under flow exception is raised.
        """
        for queue in self.queues:
            if queue:
                return queue.pop(0)
        raise UnderFlowError("All queues are empty")

    def __str__(self) -> str:
        return "\n".join(f"Priority {i}: {q}" for i, q in enumerate(self.queues))

View on GitHub (pinned to f5988cc097)

Solutions

1. Dequeue from that priority bucket before enqueueing once it is full
2. Raise the hard-coded 100 limit in the source (it appears in both FixedPriorityQueue and ElementPriorityQueue) or replace the list with collections.deque with your own policy
3. Track occupancy yourself: skip or spill items when len(pq.queues[priority]) reaches 100

Example fix

// before
for task in tasks:
    pq.enqueue(1, task)  # OverflowError at the 101st

# after
for task in tasks:
    if len(pq.queues[1]) >= 100:
        pq.dequeue()
    pq.enqueue(1, task)

if len(pq.queues[priority]) >= 100:
    pq.dequeue()  # or reject/spill
pq.enqueue(priority, data)

try:
    pq.enqueue(priority, data)
except OverflowError:
    pq.dequeue()
    pq.enqueue(priority, data)

When it happens

Trigger: Calling enqueue(priority, data) more than 100 times with the same priority value (0, 1, or 2) without intervening dequeue() calls.

Common situations: Bulk-loading more than 100 items into one priority class, forgetting that the cap is per-priority not global, or porting code from an unbounded queue.Queue.

Related errors

• Valid priorities are 0, 1, and 2
• All queues are empty
• The queue is empty
• QUEUE IS FULL
• Full Queue

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/c9b43d454123eef0. Report an issue: GitHub.