How the mount function works in fastapi when application are in two diffrent files?

Question

I have two diffrent fastaoi files.I want intergate as a single file. I have posted my code. Kindly review it and let me know your thoughts and advice.

main.py

from fastapi import FastAPI
from app import submain as subapi

app = FastAPI()
app.mount("/subapi", subapi)

@app.get("/app")
def read_main():
    return {"message": "Hello World from main app"}

submain.py

from fastapi import FastAPI

subapi = FastAPI()
@subapi.get("/sub")
async def read_sub():
    return {"message": "Hello World from sub API"}

Error

$ uvicorn app.main:app --reload
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [43148] using statreload
INFO:     Started server process [43150]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     127.0.0.1:46334 - "GET /subapi/sub HTTP/1.1" 500 Internal Server Error
ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "/home/laptop-obs-123/anaconda3/envs/albert/lib/python3.8/site-packages/uvicorn/protocols/http/h11_impl.py", line 394, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "/home/laptop-obs-123/anaconda3/envs/albert/lib/python3.8/site-packages/uvicorn/middleware/proxy_headers.py", line 45, in __call__
    return await self.app(scope, receive, send)
  File "/home/laptop-obs-123/anaconda3/envs/albert/lib/python3.8/site-packages/fastapi/applications.py", line 190, in __call__
    await super().__call__(scope, receive, send)
  File "/home/laptop-obs-123/anaconda3/envs/albert/lib/python3.8/site-packages/starlette/applications.py", line 111, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/home/laptop-obs-123/anaconda3/envs/albert/lib/python3.8/site-packages/starlette/middleware/errors.py", line 181, in __call__
    raise exc from None
  File "/home/laptop-obs-123/anaconda3/envs/albert/lib/python3.8/site-packages/starlette/middleware/errors.py", line 159, in __call__
    await self.app(scope, receive, _send)
  File "/home/laptop-obs-123/anaconda3/envs/albert/lib/python3.8/site-packages/starlette/exceptions.py", line 82, in __call__
    raise exc from None
  File "/home/laptop-obs-123/anaconda3/envs/albert/lib/python3.8/site-packages/starlette/exceptions.py", line 71, in __call__
    await self.app(scope, receive, sender)
  File "/home/laptop-obs-123/anaconda3/envs/albert/lib/python3.8/site-packages/starlette/routing.py", line 566, in __call__
    await route.handle(scope, receive, send)
  File "/home/laptop-obs-123/anaconda3/envs/albert/lib/python3.8/site-packages/starlette/routing.py", line 376, in handle
    await self.app(scope, receive, send)
TypeError: 'module' object is not callable

Kindly let me know how to mount fastapi application with in another location or another file?

Answer 1

you need to use Router see FAST API doc here
from fastapi import APIRouter

about FAST API big application

see on below:
submain.py

#!/user/bin/env python
# -*- coding: utf-8 -*-
from fastapi import APIRouter

subapi = APIRouter()

@subapi.get("/sub")
async def read_sub():
    return {"message": "Hello World from sub API"}

main.py :

#!/user/bin/env python
# -*- coding: utf-8 -*-
from fastapi import FastAPI

import submain

app = FastAPI()
app.mount("/subapi", submain)


@app.get("/app")
def read_main():
    return {"message": "Hello World from main app"}

running the code:

$ uvicorn main:app --reload
←[32mINFO←[0m:     Uvicorn running on ←[1mhttp://127.0.0.1:8000←[0m (Press CTRL+C to quit)
←[32mINFO←[0m:     Started reloader process [←[36m←[1m6616←[0m] using ←[36m←[1mwatchgod←[0m
←[32mINFO←[0m:     Started server process [←[36m1084←[0m]
←[32mINFO←[0m:     Waiting for application startup.
←[32mINFO←[0m:     Application startup complete.