Debug FastAPI application in VSCode - visual-studio-code

Question

i'm trying to debug an application (a web api) that use FastAPI (uvicorn)
I'm also using poetry and set the projev virtual environment in vscode.
i read this tutorial to setup uvicorn and this one to setup vscode but i think i'm doing something wrong in set it up.
I tried to setup the launch.json both as python: module and python: current file
The problem seems that it doesn't recognize the project structure cause when i run the debug it stopped in an import statement with this error:
Exception has occurred: ImportError
attempted relative import with no known parent package
This is my current launch.json configuration:
"configurations": [
{
"name": "Python: local debug",
"type": "python",
"request": "launch",
"program": "${workspaceFolder}/src/topic_service/service/__init__.py",
"args" : ["--port", "8000"]
},
]
I also tried to add a .env file setting PYTHONPATH:
PYTHONPATH=.:${PYTHONPATH}
Locally i run the application as follow:
poetry run uvicorn src.main:app --port 8080 --reload
Does anyone know how to correctly setup vscode to debug an uvicorn application?
Thank you
UPDATE:
I also tried what this article says. the debugger seems to start but nothing happen (no breakpoint is triggered)

Answer 1

Try this configuration.
{
"name": "Python: Module",
"type": "python",
"request": "launch",
"module": "uvicorn",
"args": ["src.main:app","--reload"]
}

Answer 2

Likewise you provide uvicorn module with necessary args during development of FastAPI application, you need to configure your launch.json located in .vscode directory with respective values.
I did a write up for custom project configurations to debug FastAPI in VS Code here
Suppose you issue the following command to run FastAPI on uvicorn server with args mentioned as below
uvicorn main:app --reload --port 8000
then your launch.json should have module with value of uvicorn and each of the args separated by space as items of the args array.
"module": "uvicorn",
"type": "python",
"request": "launch",
"args": [
"main:app",
"--reload",
"--port",
"8000"
],
"env": {
"usersecret": "some$Ecret",
}
You can have this launch.json file in .vscode and then modify the args array in the JSON configuration as per your project structure.
{
// 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",
"env": {
"db_username": "postgres",
"db_password": "secret",
"host_server": "localhost",
"database_name": "fastapi",
"ssl_mode": "prefer",
"db_server_port": "5432"
},
"args": [
"main:app",
"--reload",
"--port",
"8000"
]
}
]
}

Answer 3

For me worked with this configurations:
On Debug section on VSCode, choose create launch.json option. Probally it will open launch.json on .vscode folder in your root folder explorer
like this, inside of launch.json put this:
"version": "0.2.0",
"configurations": [
{
"name": "Python: FastAPI",
"type": "python",
"request": "launch",
"module": "uvicorn",
"cwd": "${workspaceFolder}/<folder to your main.py>",
"args": [
"main:app",
"--reload",
"--port", //these arg are optional
"3003"
]
}
]
}
Now , just run your debugger and have a nice day!
Edit: The cwd ensure that your debbuger will find the right path to your main.py file. So, for whos use multiple debuggers or uses outside vsCode with launch.json it's a nice choice use it.

Answer 4

The quick and easy way: launch debugger F5 and then select FastAPI Debug Configuration:
(p.s. this works on the VSCode Insiders; haven't tried it on a regular version)

Answer 5

The way i debug is quite basic, hope it helps
i have .py file with this config:
import uvicorn
from app.main import api
if __name__ == "__main__":
dev = 1
if dev==0:
#use this one
uvicorn.run(api, host="127.0.0.1", port=5000, log_level="info")
if dev == 1:
#or this one
uvicorn.run('app.main:api', host="127.0.0.1", port=5000, log_level="info", reload=True, debug=True)
if dev == 2:
uvicorn.run('app.main:api', host="127.0.0.1", port=5000, log_level="info", workers=2)
and run the file with the vscode debugger, the important thing is to run the app with the debug flag because otherwise the debugger skips the breakpoints (at least in my case)