Python heapq.heappushpop() Function: Usage and Examples

Push a value and remove the smallest value efficiently.

What You Will Learn

heappushpop(heap, item) performs a combined operation and may return the newly supplied item immediately if it is smaller than the current root.

Time complexity assumes a specific input structure. Include setup work such as sorting or building a lookup table when comparing complete solutions.

Step-by-Step Example

The example below makes the behavior visible with small input values that you can change safely.

import heapq
values = [3, 6, 8]
heapq.heapify(values)
print(heapq.heappushpop(values, 1))
print(values[0])

How the Example Works

The imports provide the standard-library tools used in the demonstration: heapq.
The variable values holds the result of [3, 6, 8]. Later lines use that value or inspect how it changes.
The print() calls make the return values or state visible so you can compare them with the explanation and check your prediction.

Expected output from the example:

1
3

When You Would Use This

This technique matters when a program handles larger queues, sorted records, or repeated lookups. Choose the data structure based on actual operations and the preconditions the algorithm requires. Verify boundary inputs before optimizing for speed.

Practice: Modify the Code

Maintain a min-heap of the largest k values as new data arrives.

Verify the changed output against the behavior described above, including the relevant invalid or boundary case.

For complete parameters and version details, consult the official Python documentation.

Common Beginner Mistakes

Assuming the new item will always remain in the heap after heappushpop().
Assuming the input is correctly sorted or arranged without checking the algorithm’s preconditions.

Key Takeaways

Push a value and remove the smallest value efficiently.
heappushpop(heap, item) performs a combined operation and may return the newly supplied item immediately if it is smaller than the current root.
Apply this operation only after checking the assumptions and input conditions shown in the example.