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Priority Queue with heapq

Zero-dependency Python snippets for implementing a priority queue using the standard library heapq module.

3 snippets available in this sub-category.

Simple

Min-priority queue with heapq

heap heapq priority-queue min-heap data-structures

Use (priority, value) tuples for min-priority queue

import heapq

pq = []
heapq.heappush(pq, (2, "code"))
heapq.heappush(pq, (1, "eat"))
heapq.heappush(pq, (3, "sleep"))

while pq:
    priority, task = heapq.heappop(pq)
    print(priority, task)
# 1 eat
# 2 code
# 3 sleep

Notes

  • Lower numbers = higher priority (min-heap)
  • Tuples are compared by first element (priority)

Complex

Max-priority queue with heapq

heap heapq priority-queue max-heap data-structures

Use negative priorities for max-priority queue

import heapq

pq = []
heapq.heappush(pq, (-2, "code"))
heapq.heappush(pq, (-1, "eat"))
heapq.heappush(pq, (-3, "sleep"))

while pq:
    priority, task = heapq.heappop(pq)
    print(-priority, task)
# 3 sleep
# 2 code
# 1 eat

Notes

  • Negate priorities to simulate max-heap
  • Print -priority to get original value

Priority queue with custom objects

heap heapq priority-queue custom data-structures

Use custom objects with lt for priority queue

import heapq


class Task:
    def __init__(self, priority, name):
        self.priority = priority
        self.name = name

    def __lt__(self, other):
        return self.priority < other.priority


pq = []
heapq.heappush(pq, Task(2, "code"))
heapq.heappush(pq, Task(1, "eat"))
heapq.heappush(pq, Task(3, "sleep"))

while pq:
    task = heapq.heappop(pq)
    print(task.priority, task.name)
# 1 eat
# 2 code
# 3 sleep

Notes

  • Custom objects must implement lt for heapq
  • Useful for complex priority logic

🔗 Cross Reference

🏷️ Tags

heap, heapq, priority-queue, min-heap, max-heap, custom, data-structures

📝 Notes

  • heapq is efficient for priority queues (O(log n) per operation)
  • Use (priority, value) tuples or custom objects for advanced use cases