Call async function from sync inside async FastAPI application

Question

Not sure, that this is possible, but still

I have default async FastAPI application, where I have sync function

@classmethod
def make_values(
        cls,
        records: list,
        symbol: str = None,
) -> list:
    values = []
    for record in records:
        new_row = SomePydanticModel(
            timestamp=record._mapping.get("time"),
            close=record._mapping.get("close"),
            value=record._mapping.get("value"),
        )
        if symbol in EXTRA_SYMBOLS:
            new_row = split_row(new_row, symbol)
        values.append(new_row)

    return values

The problem is that split_row is async function, that calls other async functions

async def split_row(
        row,
        symbol,
):
    adjusted_datetime = datetime.timestamp(datetime.strptime("01/01/19", "%m/%d/%y"))
    splits = await get_splits(symbol)
    # some big part with business logic with other async calls
    return row

Currently I get coroutine in new_row variable. Is there anyway to get the result of split_row?

Answer 1

One possible solution might be using Asyncer (which is on top of Anyio) introduced by Sebastian Ramirez the creator of the FastAPI. In the documentation, there's a section "Call Async Code from Sync Code".

Here's the use case:

import time
import anyio
from asyncer import asyncify, syncify

async def do_async_work(name: str):
    await anyio.sleep(1)
    return f"Hello, {name}"

def do_sync_work(name: str):
    time.sleep(1)
    message = syncify(do_async_work)(name=name)
    return message

async def main():
    message = await asyncify(do_sync_work)(name="World")
    print(message)

anyio.run(main) 

---

[NOTE]:

• As an advantage, it's also possible to use asyncio.run(main()) instead of anyio.run(main) at the end.

Answer 2

You can use an event loop to run the asynchronous function.

import asyncio

@classmethod
def make_values(cls, records: list, symbol: str = None) -> list:
    values = []
    for record in records:
        new_row = SomePydanticModel(
            timestamp=record._mapping.get("time"),
            close=record._mapping.get("close"),
            value=record._mapping.get("value"),
        )
        if symbol in EXTRA_SYMBOLS:
            loop = asyncio.get_event_loop()
            new_row = loop.run_until_complete(split_row(new_row, symbol))
        values.append(new_row)

    return values