How can I send an HTTP request from my FastAPI app to another site (API)?

@Alex Noname has made a good point of using asynchronous request library. If you want to make code faster I would suggest using asyncio.Queue as an alternate. In this example I spun up 100 producers and 100 consumers. you can limit the maximum number of messages in the queue like, then producer waits until there is space for new message

asyncio.Queue(maxsize=100)

also I have made use of AsyncClient from httpx.

If you want to know more about queues I would suggest this article https://realpython.com/async-io-python/

from time import time
from typing import List

from fastapi import FastAPI
from httpx import AsyncClient

app = FastAPI()

URL = "http://httpbin.org/uuid"
client = AsyncClient()


async def main():
    r = await client.get(URL)
    return r.text


async def producer(queue: asyncio.Queue):
    await queue.put(main)


async def consumer(queue: asyncio.Queue, resp: List):
    # await queue.get() == main  -> without arguments
    resp.append(await (await queue.get())())


async def task():
    q = asyncio.Queue(maxsize=100)
    response = []
    consumers = []
    producers = []
    [consumers.append(consumer(q, response)) for c in range(100)]
    [producers.append(producer(q)) for p in range(100)]

    await asyncio.gather(*producers)
    await asyncio.gather(*consumers)
    print(response)


@app.get('/')
def f():
    start = time()
    asyncio.run(task())
    print("time: ", time() - start)


if __name__ == '__main__':
    f()

output

['{\n  "uuid": "a7713d07-ea5d-40d3-95b4-6673f3c50a8b"\n}\n', '{\n  "uuid": "c93f8b89-2c44-40fa-9e5f-736e22ad5f23"\n}\n', '{\n  "uuid": "cbb4ad76-7790-45ae-87f1-e425eddc8021"\n}\n', '{\n  "uuid": "4c1d81c0-ae7d-401a-99df-e98af3651335"\n}\n', '{\n  "uuid": "c5f70738-fbba-4cf9-8fdf-29f8b4eabe63"\n}\n', '{\n  "uuid": "d016b852-4312-4502-a336-a6a110237d1d"\n}\n', '{\n  "uuid": "22d8b00b-4266-4236-b5a3-ed5d7c5be416"\n}\n', '{\n  "uuid": "cd54fdbb-7de9-4df3-90cc-e6b108d5fdf8"\n}\n', '{\n  "uuid": "757f0a26-7896-4a04-bea2-60c66a38b05b"\n}\n', '{\n  "uuid": "72eb6584-21f4-449b-b6bd-d0f88666126f"\n}\n', '{\n  "uuid": "b3deadf5-5b79-491b-829c-0404c306cb68"\n}\n', '{\n  "uuid": "789e7422-493d-49d2-9585-e5ca34b7cf36"\n}\n', '{\n  "uuid": "48d29a82-ff7c-41f5-8af2-42784326a31f"\n}\n', '{\n  "uuid": "84b2d67c-331c-4037-b6e4-c299d93c1899"\n}\n', '{\n  "uuid": "386e79f9-073a-4f27-961c-7befcdf95cd4"\n}\n', '{\n  "uuid": "8dfdb5e4-dd69-4043-b174-48ec8505f36f"\n}\n', '{\n  "uuid": "633e634b-b107-42bb-a7d3-c6bbfff089a0"\n}\n', '{\n  "uuid": "962d665f-8663-4be7-a3c6-9426ba500bf4"\n}\n', '{\n  "uuid": "320fb858-a751-4c34-9cdb-ddd2f4e28efa"\n}\n', '{\n  "uuid": "46a75693-5255-4ac7-8d7a-54910b4d6f68"\n}\n', '{\n  "uuid": "5323734b-7ff9-455e-ba5a-66383e6b9a1f"\n}\n', '{\n  "uuid": "622a579f-35b6-4e4b-9dba-a8a69c2049c8"\n}\n', '{\n  "uuid": "593d5e82-cef3-4be0-99ab-e3034855d7a1"\n}\n', '{\n  "uuid": "80f139df-2a27-40c1-8329-e4faa035c45c"\n}\n', '{\n  "uuid": "a97e084c-4d30-4c7b-a96e-89ed00dcfe2a"\n}\n', '{\n  "uuid": "360d49eb-7222-4064-81c2-6eba2d43a9a5"\n}\n', '{\n  "uuid": "a81b6eab-a646-4e58-b986-96a90baa52aa"\n}\n', '{\n  "uuid": "0160337e-b400-41d6-ae89-aa46c5131f40"\n}\n', '{\n  "uuid": "e600722f-8c15-4959-948b-4c4e5296feb2"\n}\n', '{\n  "uuid": "f15403e4-3674-43b2-a0c9-649fd828ba7e"\n}\n', '{\n  "uuid": "36bf139c-cc18-45a8-bc55-e7f90ce290b5"\n}\n', '{\n  "uuid": "b2368a3c-d86b-4fcd-a0d3-bf7f8f657a83"\n}\n', '{\n  "uuid": "d9f16c36-3572-4c70-8a41-3d4e279d76bf"\n}\n', '{\n  "uuid": "796087cc-a202-40dd-9921-14802a73323d"\n}\n', '{\n  "uuid": "089fa0d7-4c48-4daa-a80d-cb5ebd37dfb7"\n}\n', '{\n  "uuid": "e5582bc7-0f8a-4da7-b640-79a0d812154d"\n}\n', '{\n  "uuid": "bac0640b-0d0b-4bf2-a3c1-36bdda7cce03"\n}\n', '{\n  "uuid": "b4353004-02b2-4846-8692-33dd77ad1d3f"\n}\n', '{\n  "uuid": "1b34a744-d0ea-4acf-8bda-33743800d86a"\n}\n', '{\n  "uuid": "4d9dd269-6ee2-4356-9bc4-ddf188445320"\n}\n', '{\n  "uuid": "a1f380df-0c0d-4aee-bbb7-c3e99fbfe54f"\n}\n', '{\n  "uuid": "7cb762eb-1a42-433d-97ea-aa9de4504e35"\n}\n', '{\n  "uuid": "981c40e2-64bf-4746-8103-9430bda2a5ca"\n}\n', '{\n  "uuid": "22b778eb-82d1-48b9-9874-5ebb80ddb8b1"\n}\n', '{\n  "uuid": "e7a9e0e8-7964-400c-aafe-9c36b9b7e1a0"\n}\n', '{\n  "uuid": "21a59b91-2732-4bb6-a47e-84008a03c20c"\n}\n', '{\n  "uuid": "a78eeb39-5ecb-4509-87c2-b4a2529e3536"\n}\n', '{\n  "uuid": "4a332579-ce03-4f69-9db5-78da9196d6b2"\n}\n', '{\n  "uuid": 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"83216551-9f1b-48b2-8cd6-fd125a7ce965"\n}\n', '{\n  "uuid": "aaddb98c-879b-472d-aa39-1a684ef7d179"\n}\n', '{\n  "uuid": "4bd7e2fd-1453-4433-aa9f-bc29d82f5b9d"\n}\n', '{\n  "uuid": "b02d65e8-2063-4060-96af-088ec497fc10"\n}\n', '{\n  "uuid": "e10e3dd2-83c5-4595-afe4-4145bce79193"\n}\n', '{\n  "uuid": "8cb62784-1b5d-4dcc-8342-02ad7d417ca9"\n}\n', '{\n  "uuid": "13ef1509-4f69-4426-ac42-cb29a2d0f094"\n}\n', '{\n  "uuid": "4d4571d5-69bb-4625-b246-b5eef50aa10d"\n}\n', '{\n  "uuid": "75e7a2ca-bfa8-43b9-b33a-f3f927453579"\n}\n', '{\n  "uuid": "0a8cc8ff-2039-4873-9e38-afad3e10d726"\n}\n', '{\n  "uuid": "189ae75b-4879-4897-9725-f9be17e49844"\n}\n', '{\n  "uuid": "ba482468-f45f-4060-a0c1-3ef31bb283c8"\n}\n', '{\n  "uuid": "3809f1c7-2f11-487d-bf96-8abf64e08298"\n}\n', '{\n  "uuid": "da5ea88b-974d-4238-9654-ac56c657c8b4"\n}\n', '{\n  "uuid": "edc3de79-7cf4-42a3-a5f4-b754136a6fd3"\n}\n', '{\n  "uuid": "6f5ecd91-537c-4009-8435-6c31ce035d36"\n}\n', '{\n  "uuid": "4a33b29d-78ba-468f-8f30-a01b3d9e2a87"\n}\n', '{\n  "uuid": "a5a2ef2d-d4a2-48e1-8335-f8c1309328c4"\n}\n', '{\n  "uuid": "3d1679da-afdd-4f04-9c16-0aaea4c53d0c"\n}\n', '{\n  "uuid": "c4025845-0d4c-4549-acb8-1a249b33e644"\n}\n']
time:  1.0535461902618408

requests is a synchronous library. You need to use an asyncio-based library to make requests asynchronously.

httpx

httpx is typically used in FastAPI applications to request external services. It provides synchronous and asynchronous clients which can be used in def and async def path operations appropriately. It is also recommended for asynchronous tests of application. I would advice using it by default.

from fastapi import FastAPI
from time import time
import httpx
import asyncio

app = FastAPI()

URL = "http://httpbin.org/uuid"


async def request(client):
    response = await client.get(URL)
    return response.text


async def task():
    async with httpx.AsyncClient() as client:
        tasks = [request(client) for i in range(100)]
        result = await asyncio.gather(*tasks)
        print(result)


@app.get('/')
async def f():
    start = time()
    await task()
    print("time: ", time() - start)

Output

['{\n  "uuid": "65c454bf-9b12-4ba8-98e1-de636bffeed3"\n}\n', '{\n  "uuid": "03a48e56-2a44-48e3-bd43-a0b605bef359"\n}\n',...
time:  0.5911855697631836

aiohttp

aiohttp can also be used in FastAPI applications, if you prefer one.

from fastapi import FastAPI
from time import time
import aiohttp
import asyncio

app = FastAPI()

URL = "http://httpbin.org/uuid"


async def request(session):
    async with session.get(URL) as response:
        return await response.text()


async def task():
    async with aiohttp.ClientSession() as session:
        tasks = [request(session) for i in range(100)]
        result = await asyncio.gather(*tasks)
        print(result)


@app.get('/')
async def f():
    start = time()
    await task()
    print("time: ", time() - start)

---

If you want to limit the number of requests executing in parallel, you can use asyncio.semaphore like so:

MAX_IN_PARALLEL = 10
limit_sem = asyncio.Semaphore(MAX_IN_PARALLEL)


async def request(client):
    async with limit_sem:
        response = await client.get(URL)
        return response.text