python priority queue customized comparator

Python priority queue customized comparator how to#

Since pairs are compared lexicographically, this means that data will be placed in increasing order of priority. Here, we insert the pair (priority, data). The function inserts the second argument in the list so that the list remains sorted in logarithmic (O(log( N))) time. Its insort() method is called with a first argument that is a currently sorted list and an arbitrary second argument. The module is called bisect because it uses a basic bisection algorithm to do its work.

The bisect module, from the standard Python library, is very handy for maintaining a sorted list without having to sort the list after each insertion.

Python priority queue customized comparator how to#

Let’s see an example of how to use the above-created priority queue. Heapq.heappush(self._queue, (-priority, self._index, item)) The following python program uses the heapq module to implement a simple priority queue: import heapq heappop(): pops and returns the smallest item from the heap, maintaining the heap invariant.heappush(): pushes the value item onto the heap, maintaining the heap invariant.We use the following methods to push and pop the queue elements: Heaps are binary trees for which every parent node has a value less than or equal to any of its children, the smallest element is always the root, heap. The heapq module provides an implementation of the heap queue algorithm, also known as the priority queue algorithm. Now we can use the queue.put() and queue.get() methods to push and pop elements from the queue. If the queue elements are not comparable, the data can be wrapped in a class (such as tuples) that ignores the data item and only compares the priority number: from dataclasses import dataclass, field It provides the best and worst case performance with time complexity of O(log n). This priority queue can accept the comparable items and the lowest valued entries are retrieved first. The queue module has inbuilt class PriorityQueue. The main difference between a regular queue and priority queue is that a regular queue serve the elements in FIFO order where as a priority queue elements are served on the basis of priority. The priority queues are used in several usecases, such as job scheduling algorithms and message processing systems. If two elements have the same priority, they are served according to their order in the priority queue. In a priority queue, an element with high priority is served before an element with low priority. The priority queue is an abstract data type that is like a regular queue, but each element in the queue has a “priority” associated with it.