Fastapi: [QUESTION] How to get async functionality to work?

Created on 7 Feb 2020 · 6Comments · Source: tiangolo/fastapi

First check

[x] I used the GitHub search to find a similar issue and didn't find it.
[x] I searched the FastAPI documentation, with the integrated search.
[x] I already searched in Google "How to X in FastAPI" and didn't find any information.

Description

How can I properly utilize the asynchronous within a route? The following code takes 4 seconds to complete a call to /async route, while I expect it to only take 2 seconds.

import time
from fastapi import FastAPI

app = FastAPI()

async def get_a():
    time.sleep(2)
    return 'a'

async def get_b():
    time.sleep(2)
    return 'b'

@app.get("/async")
async def asynchronous():
    a = await get_a()
    b = await get_b()
    return {
        'a': a,
        'b': b,
    }

Additional context

Environment is running off docker container tiangolo/uvicorn-gunicorn-fastapi:python3.7
App was was started with uvicorn app.app:app --reload --host 0.0.0.0

Add any other context or screenshots about the feature request here.

question

Source

jscottcronin

Most helpful comment

@euri10 - asyncio.sleep did work.

Instead of writing a dummy function like

async def get_b():
    asyncio.sleep(2)
    return 'b'

How would I write a function that makes requests like the following. Note: this request takes 2x as long as I expect, where each request takes about the same amount of time. I have tried with both requests and httpx libraries.

async def get_taxonomy():
    return httpx.post(TAXONOMY_ENDPOINT, json=TAXONOMY_PAYLOAD).json()

async def get_attributes():
    return httpx.post(ATTRIBUTE_ENDPOINT, json=ATTRIBUTE_PAYLOAD).json()

@app.get("/async")
async def asynchronous():
    return {
        'taxonomy': await get_taxonomy(),
        'attributes': await get_attributes(),
    }

jscottcronin on 7 Feb 2020

👍2

All 6 comments

time.sleep blocks
Use asyncio.sleep

Le ven. 7 févr. 2020 à 9:03 PM, Scott Cronin notifications@github.com a
écrit :

First check

I used the GitHub search to find a similar issue and didn't find it.

I searched the FastAPI documentation, with the integrated search.

I already searched in Google "How to X in FastAPI" and didn't find
any information.

Description

How can I properly utilize the asynchronous within a route? The following
code takes 4 seconds to complete a call to /async route, while I expect
it to only take 2 seconds.

import timefrom fastapi import FastAPI

app = FastAPI()
async def get_a():
time.sleep(2)
return 'a'
async def get_b():
time.sleep(2)
return 'b'
@app.get("/async")async def asynchronous():
a = await get_a()
b = await get_b()
return {
'a': a,
'b': b,
}

Additional context

Environment is running off docker container
tiangolo/uvicorn-gunicorn-fastapi:python3.7
App was was started with uvicorn app.app:app --reload --host 0.0.0.0

Add any other context or screenshots about the feature request here.

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euri10 on 7 Feb 2020

@euri10 - asyncio.sleep did work.

Instead of writing a dummy function like

async def get_b():
    asyncio.sleep(2)
    return 'b'

async def get_taxonomy():
    return httpx.post(TAXONOMY_ENDPOINT, json=TAXONOMY_PAYLOAD).json()

async def get_attributes():
    return httpx.post(ATTRIBUTE_ENDPOINT, json=ATTRIBUTE_PAYLOAD).json()

@app.get("/async")
async def asynchronous():
    return {
        'taxonomy': await get_taxonomy(),
        'attributes': await get_attributes(),
    }

jscottcronin on 7 Feb 2020

👍2

https://www.python-httpx.org/async/

phy25 on 7 Feb 2020

This is a "how to use asyncio in Python" and is unrelated to FastAPI.

The await keyword blocks the execution of the remaining code in the function, so each await causes the code in that function to execute synchronously (await causes the event loop to execute the next event scheduled on the event loop).

You will want to use asyncio.create_task() or asyncio.gather() to schedule and execute coroutines on the event loop. This will allow both httpx methods to make their requests and wait for their responses in an asynchronous manner.

Note: If you are used to Javascript async/await or promises, the Python asyncio machinery does not function in quite the same manner.