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Retries and Backoff

Introduction​

In this tutorial, we will discuss handling errors and exceptions in Python's requests library with a focus on 'retries and backoff.' This is a crucial aspect of any application that communicates with external services or APIs. Let's explore what these terms mean and how to implement them using Python.

Understanding Retries and Backoff​

'Retry' is a process where your program tries to execute a failing operation again in the hope that it might succeed. 'Backoff' is a delay between retry attempts. It's usually a good practice to gradually increase this delay (exponential backoff) to avoid overwhelming the server or network.

Why Retry and Backoff?​

Networks are unpredictable. A request might fail due to temporary issues like network congestion, server overload, brief downtime, etc. By implementing retries and backoff, we can make our application more resilient to these transient errors.

Implementing Retries in requests​

The requests library doesn't directly support retries, but it provides a way to do so through the Session object and HTTPAdapter. Here's a basic example:

from requests import Session
from requests.adapters import HTTPAdapter

s = Session()
adapter = HTTPAdapter(max_retries=3)
s.mount('http://', adapter)
s.mount('https://', adapter)

response = s.get('http://example.com')

In the above code, max_retries=3 means that the Session will make three attempts to send the request if it fails initially.

Implementing Backoff​

For adding backoff to our retries, we can use the Retry object from urllib3, a library that requests uses under the hood. Here's how:

from requests import Session
from requests.adapters import HTTPAdapter
from urllib3.util import Retry

retry_strategy = Retry(
    total=3,
    backoff_factor=1,
    status_forcelist=[429, 500, 502, 503, 504],
    method_whitelist=["HEAD", "GET", "OPTIONS"]
)

adapter = HTTPAdapter(max_retries=retry_strategy)
s = Session()
s.mount("http://", adapter)
s.mount("https://", adapter)

response = s.get('http://example.com')

Here, backoff_factor controls the delay between retries. status_forcelist is a list of HTTP status codes that we should retry upon. method_whitelist specifies for which HTTP methods to retry.

Conclusion​

Implementing retries and backoff in your Python applications using requests can make your application more robust and less prone to failure. It's a best practice to always consider these strategies when dealing with network requests. Happy coding!

This tutorial covers the basic usage of retries and backoff in the requests library. It should be a good starting point for beginners seeking to improve the robustness of their network applications.