TopolearnEvery aiohttp client program is built around one long-lived session, so the pattern has to be right from the start.
aiohttp is async-only: every request is awaited inside a coroutine run by asyncio. Install it with pip install aiohttp.
The central object is aiohttp.ClientSession. It owns a connection pool, cookies and default settings, and it must be created inside a running event loop (inside an async def) and closed when you are done. The idiom is nested async with blocks:
async with aiohttp.ClientSession() as session:
async with session.get(url) as resp:
data = await resp.json()The outer block closes the session and its connections. The inner block makes the request: session.get(...) sends it and returns once the status line and headers have arrived; the body is read separately with await resp.text(), await resp.json() or await resp.read(). Leaving the inner block releases the connection back to the pool.
Methods mirror HTTP verbs: session.get, post, put, patch, delete, head, options, plus session.request(method, url). Data options include params=, headers=, json= and data=.
Rules from the official docs: create one session per application (or per group of related requests) and reuse it; do not create a session per request, which throws away connection pooling and is slow. Also, there is no top-level aiohttp.get function for good reason: always go through a session.
To start the program, call asyncio.run(main()).
Example
import asyncio
import aiohttp
async def main():
async with aiohttp.ClientSession() as session:
async with session.get("https://httpbin.org/get", params={"q": "aio"}) as resp:
print(resp.status) # 200
data = await resp.json()
print(data["args"]) # {'q': 'aio'}
async with session.post("https://httpbin.org/post", json={"x": 1}) as resp:
print((await resp.json())["json"]) # {'x': 1}
asyncio.run(main())Remember
- Create one ClientSession inside async code and reuse it
- async with session.get(...) as resp, then await resp.json()/text()/read()
- Leaving the blocks releases connections and closes the session
Watch out for
- Creating a new ClientSession for every request.