CODEWITHSUNDEEP
pythonfastapiuvicorn
Pokisutra
Pokisutra

Reputation: 1731

FastAPI throws an error (Error loading ASGI app. Could not import module "api")

I tried to run FastAPI using uvicorn webserver but it throws an error.

I run this command,

uvicorn api:app --reload --host 0.0.0.0

but there is an error in the terminal.

Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)
Started reloader process [23445]
Error loading ASGI app. Could not import module "api".
Stopping reloader process [23445]

Upvotes: 171

Views: 308495

Answers (16)

Ssali Jonathan
Ssali Jonathan

Reputation: 97

If you are reading this in August of 2024 and beyond, FastAPI now has a CLI utility for running your app.

fastapi <subcommand>

To run your app in development

fastapi dev <file or package where your FastAPI app instance is>

To run your app in production

fastapi run <file or package where your FastAPI app instance is>

So FastAPI will under the hood take care of the uvicorn command stuff for you

Upvotes: 2

Georgios Syngouroglou
Georgios Syngouroglou

Reputation: 19944

Except of the accepted answer, there is another way (as always), which let you load an application from whichever location. For example, for a directory structure like this,

/home/my_user/project_folder/
├── some_folder
├── src
│   └── main.py
└── tests
    ├── test_xx.py
    └── test_yy.py

you may run like the following (check the terminal location!):

# Two ways to run it from outside of the project dir:
/home> uvicorn --app-dir ./my_user/project_folder/src main:app --reload
/home> uvicorn my_user.project_folder.src.main:app --reload

# Two ways to run it from outside of the project dir:
/home/my_user> uvicorn --app-dir ./project_folder/src main:app --reload
/home/my_user> uvicorn project_folder.src.main:app --reload

# Two ways to run it from the project root:
/home/my_user/project_folder> uvicorn --app-dir ./src main:app --reload
/home/my_user/project_folder> uvicorn src.main:app --reload

# From the same level with you main.py file:
/home/my_user/project_folder/src> uvicorn main:app --reload

Upvotes: 1

MD SHAYON
MD SHAYON

Reputation: 8055

  • Step-1 make sure your main file is located in the same directory of your terminal/command prompt, use ls command
(virtual-env) shayon@shayon-X556UQK:~/Documents/python-fast-api$ ls
main.py  __pycache__  README.md  requirements.txt  virtual-env
  • Step-2 check the directory of your terminal using pwd command
(virtual-env) shayon@shayon-X556UQK:~/Documents/python-fast-api$ pwd
/home/shayon/Documents/python-fast-api
  • Step-3 check the name of your object - here app is the object of FastAPI so we need to use the command uvicorn main:app --reload, if you keep the object name app1 you need to run uvicorn main:app1 --reload
(virtual-env) shayon@shayon-X556UQK:~/Documents/python-fast-api$ cat main.py

main.py

from fastapi import FastAPI
app = FastAPI()


@app.get("/")
def index():
    return {"Hello": "World"}
  • Step-4 In my case, I made a mistake making command of uvicorn main.py:app --reload and this was the reason for my error. The command should be uvicorn main:app --reload (without dot py extension)

Upvotes: 2

Jithu the menjoker
Jithu the menjoker

Reputation: 1

don't give the same name for your python file like uvicorn.py,Folder same name, package name

Upvotes: 0

Spinstaz
Spinstaz

Reputation: 331

I fixed this by using the following in my main:

import uvicorn

app = FastAPI()

@app.get("/")
def index():
    return {"index": "root"}

if __name__ == '__main__':

    uvicorn.run(f"{Path(__file__).stem}:app", host="127.0.0.1", port=8888, reload=True)

and then from the terminal, I typed uvicorn main:app --reload as my main.py is in my root folder.

Upvotes: 1

MarthaX
MarthaX

Reputation: 31

I also encountered the same issue, being a total beginner to FastAPI, the solution given by Yagiz Degirmenci helped to come up with a simple idea for beginners like me, i.e

cd directory of code
uvicorn fast-api:main --reload

PS. fast-api is the name of my file (i.e fast-api.py)

Upvotes: 3

svs
svs

Reputation: 63

If you are using Pycharm , the reason could be the source directory not being set correctly. For example, I was trying to configure Python remote debugger using docker-compose and my folder structure was like this:

my_app_name
├── docker-compose.yml
├── src
│   └── main.py
└── tests
    ├── test_file1.py
    └── test_file2.py

I had the src folder inside the root folder, which contained the main.py file. In PyCharm project settings, by default your source folder is set to root.But if you have a nested structure like the case above, you have to go to Preferences->Project->Project Structure->Sources and add your src folder under Source Folders.

Upvotes: 0

fudu
fudu

Reputation: 742

Also another reason for this error:

There's already a file named exactly like your running folder, then it will make a conflict to the system.

Example you have a file inside a folder named test_app/main.py, then you should run uvicorn test_app.main:app --reload to run the app.

But, if you have a file named test_app.py (which is the same name as the folder above), it will throw the error when you run the app.

enter image description here

So the solution is to rename the folder or rename the file so they won't be conflict to each other.

Upvotes: 0

Tonatio
Tonatio

Reputation: 4198

Another reason for this error: there is a circular reference between files.

Example:

  • main.py:

    from tools import validator

# ...

class GlobalException(Exception):
    # ...

  • /tools/validator.py:

    from main import GlobalException

Upvotes: 4

user
user

Reputation: 5696

One reason this might be happening is that you are using:

uvicorn src/main:app --reload

instead of the correct syntax:

uvicorn src.main:app --reload

Notice the . instead of the /
Currently auto-completion in the terminal suggests the wrong format.

That's assuming that:

(1) your structure is something like this:

project_folder/
├── some_folder
├── src
│   └── main.py
└── tests
    ├── test_xx.py
    └── test_yy.py

(2) your FastAPI() object is indeed assigned to an object named app in main.py:

app = FastAPI()

(3) you are running the uvicorn command from the project_folder, e.g.:

(venv) <username>@<pcname>:~/PycharmProjects/project_folder$ uvicorn src.main:app --reload

Upvotes: 23

Ajay Tom George
Ajay Tom George

Reputation: 2279

Use this folder structure and configuration where main is in parent directory enter image description here

launch.json

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Python: FastAPI",
            "type": "python",
            "request": "launch",
            "module": "uvicorn",
            "args": [
                "main:app"
            ],
            "jinja": true
        }
    ]
}

main.py

from fastapi import FastAPI
app = FastAPI(
    title="test",
    description="test",
    version="0.0.1",
)
if __name__ == "__main__":
import uvicorn

uvicorn.run(
    "main:app",
    host="0.0.0.0",
    reload=True,
    port=3001,
)

Upvotes: 0

Gul Saeed Khattak
Gul Saeed Khattak

Reputation: 209

Hit the Save button in VS Code etc because sometimes it will throw this error if you have not saved the file. Happened to me.

Upvotes: 1

Avik Jain
Avik Jain

Reputation: 221

It seems it is important that you name your file main.py otherwise it won't work.

Edit: Actually I was running Jupyter Notebook on port 8888 so that port was already occupied. If you have to run Jupyter notebook, run it after running the API server, the notebook will automatically run on 8889. Alternatively, you can run the API server on a different port.

Upvotes: 2

bbartling
bbartling

Reputation: 3494

This worked for me look at the docs for fastAPI. I am very thankful I ran accross that as the Python script needs to be named main.py not app.py

The command uvicorn main:app refers to:

  1. main: the file main.py (the Python "module").
  2. app: the object created inside of main.py with the line app = FastAPI()
  3. --reload: make the server restart after code changes. Only use for development.

Upvotes: 5

cjeronimomx
cjeronimomx

Reputation: 875

I had the same problem and solved it adding package name before main, in your case trying:

uvicorn src.main:app --reload

may solve the problem

Upvotes: 12

Yagiz Degirmenci
Yagiz Degirmenci

Reputation: 20598

TL;DR

Add the directory name in front of your filename

uvicorn src.main:app

or cd into that directory

cd src
uvicorn main:app

Long Answer

It happens because you are not in the same folder with your FastAPI app instance more specifically:

Let's say i have an app-tree like this;

my_fastapi_app/
├── app.yaml
├── docker-compose.yml
├── src
│   └── main.py
└── tests
    ├── test_xx.py
    └── test_yy.py

$ pwd         # Present Working Directory
/home/yagiz/Desktop/my_fastapi_app

I'm not inside the same folder with my app instance, so if I try to run my app with uvicorn I'll get an error like yours

$ uvicorn main:app --reload
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [40645] using statreload
ERROR:    Error loading ASGI app. Could not import module "main".

The answer is so simple, add the folder name in front of your filename

uvicorn src.main:app --reload

or you can change your working directory

cd src

Now i'm inside of the folder with my app instance

src
└── main.py

Run your uvicorn again

$ uvicorn main:app --reload
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [40726] using statreload
INFO:     Started server process [40728]
INFO:     Waiting for application startup.
INFO:     Application startup complete.

Upvotes: 316

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