How do I use heapq for priority queues in Python?

How do I use heapq for priority queues in Python?

You can use the heapq module in Python to implement priority queues. It provides an efficient way to maintain a priority queue using a binary heap.

Can you show me a simple example?

Sure! Here's a basic example:

import heapq

# Create an empty priority queue
priority_queue = []

# Add items with their priority
heapq.heappush(priority_queue, (2, 'task 2'))
heapq.heappush(priority_queue, (1, 'task 1'))
heapq.heappush(priority_queue, (3, 'task 3'))

# Pop items in order of priority
while priority_queue:
    priority = heapq.heappop(priority_queue)
    print(priority)

This will print tasks in order of their priority.

What if I want to change the priority of an existing task?

You can't directly change the priority of an item in the heap. Instead, you can remove the item, change its priority, and then push it back into the heap.

Is there a way to implement a max-heap using heapq?

Yes! You can simulate a max-heap by pushing negative values into the min-heap. For example, push -priority instead of priority.