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

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

httpx

httpx.AsyncClient is typically used in FastAPI applications to request external services. It is also used for asynchronous tests of application. Use it by default.

from fastapi import FastAPIfrom time import timeimport httpximport asyncioapp = FastAPI()URL = "http://httpbin.org/uuid"async def request(client):    response = await client.get(URL)    return response.textasync 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, but do so if you really need it.

from fastapi import FastAPIfrom time import timeimport aiohttpimport asyncioapp = 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 = 10limit_sem = asyncio.Semaphore(MAX_IN_PARALLEL)async def request(client):    async with limit_sem:        response = await client.get(URL)        return response.text

@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 articlehttps://realpython.com/async-io-python/

from time import timefrom typing import Listfrom fastapi import FastAPIfrom httpx import AsyncClientapp = FastAPI()URL = "http://httpbin.org/uuid"client = AsyncClient()async def main():    r = await client.get(URL)    return r.textasync 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": "55fbc34f-4eb3-4356-98e3-1df38054a4b2"\n}\n', '{\n  "uuid": "257ac454-09c2-4fd4-bdb3-303495360fa2"\n}\n', '{\n  "uuid": "7505cc0d-01b3-47f8-91d4-3e54d0f387de"\n}\n', '{\n  "uuid": "0fd67af2-622e-4688-b3c8-f64e20f1f3ec"\n}\n', '{\n  "uuid": "07653ccf-f408-4807-8ff5-e6098d657451"\n}\n', '{\n  "uuid": "b9d0ff18-fd67-4afa-adbe-ebcb53380804"\n}\n', '{\n  "uuid": "70d4d53b-2f06-41be-bb38-47f010cfa40f"\n}\n', '{\n  "uuid": "a6d49873-e749-4578-ae9c-e6c6f473535d"\n}\n', '{\n  "uuid": "e67efee5-76ad-4812-bb97-016ef9ff87e8"\n}\n', '{\n  "uuid": "67886926-b2d9-44fb-b836-26b81c53e5fb"\n}\n', '{\n  "uuid": "dcbd4ff8-e3cd-4e03-b12d-5fb3834b0e00"\n}\n', '{\n  "uuid": "65c2eaee-5fa2-4b58-a1c3-adeb04d92c71"\n}\n', '{\n  "uuid": "2cee4ec9-952e-45c5-91b7-f4f5848c3455"\n}\n', '{\n  "uuid": "8e94bf1c-ee5a-483a-a962-d0b9aea48c95"\n}\n', '{\n  "uuid": "c1fe17bc-bedf-4c4c-952d-a5921f693d9f"\n}\n', '{\n  "uuid": "221456fd-48ca-4826-a8b5-5fa0b23db6e4"\n}\n', '{\n  "uuid": "62fda759-b382-44e4-ad7d-d19a952fc1c7"\n}\n', '{\n  "uuid": "73faeb91-215e-4e49-8f11-11b98e499cc7"\n}\n', '{\n  "uuid": "f3279c45-ebcc-4079-b823-3efe825c7cf8"\n}\n', '{\n  "uuid": "b892672b-4510-44f4-b61e-9cccaa52421e"\n}\n', '{\n  "uuid": "8926979d-71a7-4171-9389-ddafff89e229"\n}\n', '{\n  "uuid": "d97cef59-4862-42ca-b0f2-261f98fd4b6f"\n}\n', '{\n  "uuid": "3362ff93-89e4-4889-a2f2-2e03771e86ce"\n}\n', '{\n  "uuid": "9f525251-4fe4-4a9c-97b5-2f01d2b37aaf"\n}\n', '{\n  "uuid": "036959d4-3179-40f9-bbf3-32274f2cede2"\n}\n', '{\n  "uuid": "157f8c22-6214-4e27-ab5d-08d39f96d1d3"\n}\n', '{\n  "uuid": "e4bfbf62-7c33-4fd7-a231-47f5ce398041"\n}\n', '{\n  "uuid": "a41512c1-3346-4457-a379-64d690ffc2ea"\n}\n', '{\n  "uuid": "7bb07cfb-294b-44fa-a8dc-6d283c54409f"\n}\n', '{\n  "uuid": "f2297d22-a2d0-47ff-8d65-24c6fe7877a7"\n}\n', '{\n  "uuid": "645e255b-4c93-4c8f-9ff2-43da293db660"\n}\n', '{\n  "uuid": "9190e370-dfa9-47a6-8cef-8df7ab762433"\n}\n', '{\n  "uuid": "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