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requests & httpx — Calling APIs

Intermediate

Important Libraries

requests is the de-facto HTTP client: get/post with params and JSON, status checks with raise_for_status, timeouts ALWAYS, and Sessions for connection reuse.

Overview

Every backend consumes other services — payment gateways, auth providers, internal microservices — and in Python that means requests (sync) or httpx (same API, plus async). The non-negotiables of production HTTP: pass timeout= on every call (the default is wait-forever), check responses with raise_for_status(), send/receive JSON via json= and .json(), and reuse a Session for connection pooling and shared headers. These five habits are what code reviewers look for first.

GET & POST with JSON

params= builds the query string safely; json= serializes the body and sets Content-Type. Inspect status_code, headers and .json(). raise_for_status() turns 4xx/5xx into exceptions.

The production checklist: timeout, raise_for_status, json=

import requests

# GET with query parameters
r = requests.get(
    "https://api.github.com/search/repositories",
    params={"q": "fastapi", "per_page": 3},   # ?q=fastapi&per_page=3
    timeout=10,                                # ALWAYS set a timeout
)
r.raise_for_status()                           # raises on 4xx/5xx
data = r.json()                                # parsed JSON body
print(r.status_code, data["total_count"])

# POST JSON
payload = {"name": "Asha", "plan": "pro"}
r = requests.post(
    "https://httpbin.org/post",
    json=payload,                              # serializes + sets header
    headers={"Authorization": "Bearer TOKEN"},
    timeout=10,
)
print(r.json()["json"])                        # {'name': 'Asha', 'plan': 'pro'}

# Error handling that distinguishes failure modes
try:
    r = requests.get("https://api.example.com/health", timeout=5)
    r.raise_for_status()
except requests.Timeout:
    print("service too slow")
except requests.HTTPError as e:
    print("bad status:", e.response.status_code)
except requests.ConnectionError:
    print("network/DNS problem")

Sessions, Retries & httpx/async

A Session reuses TCP connections (much faster for many calls) and carries default headers. httpx mirrors the API and adds async — the natural pair for FastAPI services.

Session + Retry; httpx when you need async

import requests
from requests.adapters import HTTPAdapter, Retry

session = requests.Session()
session.headers.update({"Authorization": "Bearer TOKEN"})

# Automatic retries with backoff for flaky upstreams
retries = Retry(total=3, backoff_factor=0.5,
                status_forcelist=[502, 503, 504])
session.mount("https://", HTTPAdapter(max_retries=retries))

for page in range(1, 4):                     # pooled connections
    r = session.get("https://api.example.com/items",
                    params={"page": page}, timeout=10)

# httpx — same feel, plus async (used inside FastAPI)
# import httpx, asyncio
# async def fetch_all(urls):
#     async with httpx.AsyncClient(timeout=10) as client:
#         responses = await asyncio.gather(*(client.get(u) for u in urls))
#         return [r.json() for r in responses]
# ^ 20 API calls in the time of the slowest one — not the sum

Key Points to Remember

1ALWAYS pass timeout= — the default waits forever and hangs services
2raise_for_status() converts 4xx/5xx into catchable HTTPError
3json= to send, .json() to receive; params= builds query strings safely
4Session = pooling + shared headers + retry mounting; httpx = same API + async

Interview Questions

What happens if you skip timeout on requests.get in a web service?

MediumRazorpay

Difference between data= and json= in requests.post?

MediumZomato

When would you pick httpx over requests?

MediumSwiggy

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