python 30 lines · 7 steps

Building a resilient requests Session

A reusable HTTP session with automatic retries and backoff keeps flaky API calls from failing on the first hiccup.

Explained by highlit
Intermediate retries backoff http-client resilience connection-pooling
1import requests
2from requests.adapters import HTTPAdapter
3from urllib3.util.retry import Retry
4 
5 
6def build_session() -> requests.Session:
7 session = requests.Session()
8 retries = Retry(
9 total=4,
10 backoff_factor=0.5,
11 status_forcelist=(429, 500, 502, 503, 504),
12 allowed_methods=frozenset({"POST", "GET"}),
13 raise_on_status=False,
14 )
15 adapter = HTTPAdapter(max_retries=retries)
16 session.mount("https://", adapter)
17 session.mount("http://", adapter)
18 session.headers.update({"User-Agent": "billing-sync/1.0"})
19 return session
20 
21 
22def submit_invoice(session: requests.Session, invoice: dict, token: str) -> dict:
23 response = session.post(
24 "https://api.acme.example/v2/invoices",
25 json=invoice,
26 headers={"Authorization": f"Bearer {token}"},
27 timeout=(3.05, 27),
28 )
29 response.raise_for_status()
30 return response.json()
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1Configuring retries at the adapter level means every request through the session inherits the same resilience policy.
  2. 2Exponential backoff with a status_forcelist retries only transient failures instead of blindly hammering the server.
  3. 3Always pair requests with explicit connect and read timeouts so a hung server can't stall your process indefinitely.

Related explainers

python 
from fastapi import FastAPI, WebSocket, WebSocketDisconnect
 
app = FastAPI()
 

Building a WebSocket chat with FastAPI

websockets broadcast connection-management
Intermediate 9 steps
python 
import time
import uuid
 
from django.utils.deprecation import MiddlewareMixin

Attaching per-request context in Django

middleware request lifecycle multi-tenancy
Intermediate 7 steps
python 
import random
from typing import Iterator, List
 
 

How reservoir sampling picks k items

reservoir-sampling streaming randomness
Intermediate 5 steps
python 
import secrets
 
from django.contrib.auth import authenticate, login
from django.core.cache import cache

Two-factor login with OTP in Django

two-factor-auth one-time-passwords caching
Intermediate 9 steps
typescript 
import { Injectable, Scope, Inject, NotFoundException } from '@nestjs/common';
import { REQUEST } from '@nestjs/core';
import { Request } from 'express';
import { DataSource } from 'typeorm';

Per-tenant database connections in NestJS

multi-tenancy connection-pooling dependency-injection
Advanced 8 steps
python 
import re
from functools import total_ordering
from typing import Optional
 

Parsing and comparing semantic versions

regex operator-overloading sorting
Intermediate 7 steps

Share this explainer

Here's the card — post it anywhere.

Building a resilient requests Session — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code