FastAPI cannot find my Python Package. It seems relatively obvious that this is an issue with Python paths and imports, however I do not know how to fix it.

What surprised me is that this worked when using Flask instead of FastAPI. I converted a small application from Flask to FastAPI, and this is when the import statements no longer were able to find my Python package.

I don’t know enough about the FastAPI-cli to understand what it does / does not do with paths to know how to fix it.

Here’s a very simple MWE.

# /fastapi/fastapi_mwe.py

from fastapi import FastAPI
from pydantic import BaseModel

from my_package import my_value

print(f'__name__={__name__}')
app = FastAPI()

class FastAPI_Value(BaseModel):
    value: int

@app.get('/')
def root(fastapi_value: FastAPI_Value):
    next_value = fastapi_value.value + my_value
    return {
        'next_value': next_value
    }

# /my_package/__init__.py

my_value = 1

Here’s the project structure:

stack_overflow_mwe/
    my_package/
        __init__.py
    fastapi/
        fastapi_mwe.py

Here’s how I run fastapi_mwe.py:

user@host:/home/user/stackoverflow_mwe/$ fastapi dev fastapi/fastapi_mwe.py
ModuleNotFoundError: No module named `my_package`

How should I structure this project and how can I fix this? I don’t really want to put the package my_package into the subdirectory fastapi, because this package should be totally independent of the fastapi wrapper/webserver. I should be able to create a new subfolder called flask_api and be able to import my_package from both locations.

I have also tried to avoid using .venv and an editable install + pyproject.toml. I am using virtual environments to manage dependencies (for example I did pip3 install fastapi to install the fastapi package into a local .venv). If there is no alternative, then I can create a pyproject.toml and setup the local packages as an editable install, but I don’t really want to do this unless there is no alternative.