Make it possible to run fastapi run with a module instead of a path

[barraponto]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched in the documentation/README.
• I already searched in Google "How to do X" and didn't find any information.
• I already read and followed all the tutorial in the docs/README and didn't find an answer.

Commit to Help

• I commit to help with one of those options 👆

Example Code

def get_import_data(
    *, path: Union[Path, None] = None, app_name: Union[str, None] = None
) -> ImportData:
    if not path:
        path = get_default_path()

    logger.debug(f"Using path [blue]{path}[/blue]")
    logger.debug(f"Resolved absolute path {path.resolve()}")

    if not path.exists():
        raise FastAPICLIException(f"Path does not exist {path}")
    mod_data = get_module_data_from_path(path)
    sys.path.insert(0, str(mod_data.extra_sys_path))
    use_app_name = get_app_name(mod_data=mod_data, app_name=app_name)

    import_string = f"{mod_data.module_import_str}:{use_app_name}"

    return ImportData(
        app_name=use_app_name, module_data=mod_data, import_string=import_string
    )

Description

Let's say you have your fastapi app packaged up and available in the awesomeapi package.
Wouldn't it be nice if you could run fastapi run awesomeapi:app just like you can do with uvicorn awesomeapi:app?

Operating System

Linux

Operating System Details

Python 3.12

Python Version

3.12

Additional Context

No response

[barraponto]

The mentioned code is from fastapi_cli.discover.get_import_data.
I brought it up to highlight how it eagerly looks for a path and:

• if path is not found, immediately aborts with an error
• if path is found, it builds up the package:object module path and uses it!!

[barraponto]

FWIW, uvicorn has a very handy method to load the app from a module:obj string: https://github.com/encode/uvicorn/blob/master/uvicorn/importer.py#L9

[TakodaS]

This is incredibly important since running fastapi with a directory structure
pyproject.toml
app/
|_ init.py
|_ main.py
|_ routes/
|_ ...
|_

will require modification of all module imports from something like from app.routes.foo import bar to from routes.foo import bar since the python path is set to app/. One can break the monolithic app pattern by moving main.py to the top-level and this will work, but it would be much better to run as a module like with uvicorn app.main:app and have the imports work as expected.

[ericgtkb]

This feature will be extremely useful especially for the use case where the application code is packaged using pyproject.toml + src layout (+ potentially also namespace package). For example:

project-root/
|-- pyproject.toml
|-- src/
|    |-- my_ns_package/
|    |    |-- my_package/
|    |    |    |-- __init__.py
|    |    |    |-- main.py        <-- app is there
|    |    |    |-- <other-modules>.py

In uses cases like this we often pip install <app-repo>, so the source code likely not even in the current working directory. Be able to run with fastapi run my_ns_package.my_package.main:app would be extremely useful for this use case.