Idempotency in APIs: How to Handle Retries Safely (Python Example)

What happens if a user clicks “Pay Now” twice? Or if a network timeout causes a request to retry automatically? Without Idempotency, your API might process that payment twice.

In this video, we explore the concept of Idempotency in API design—a critical property that ensures performing an operation multiple times produces the same result as doing it once. We look at which HTTP methods are naturally safe, how to fix those that aren’t (like POST), and how to implement Idempotency Keys to handle network retries without corrupting your data.

In this video, we cover:

* The definition of Idempotency and why it matters for distributed systems.

* Which HTTP methods (GET, POST, PUT, DELETE) are safe and which are dangerous.

* The problem with network retries and duplicate transactions.

* How to use Idempotency Keys in headers to “remember” previous requests.

* A practical Python/Flask code example showing how to build a safe payment endpoint.