python-multipart package changed it's namespace, hence fastapi fails

[fingineering]

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Example Code

def ensure_multipart_is_installed() -> None:
    try:
        # __version__ is available in both multiparts, and can be mocked
        from multipart import __version__

        assert __version__
        try:
            # parse_options_header is only available in the right multipart
            from multipart.multipart import parse_options_header

            assert parse_options_header  # type: ignore[truthy-function]
        except ImportError:
            logger.error(multipart_incorrect_install_error)
            raise RuntimeError(multipart_incorrect_install_error) from None
    except ImportError:
        logger.error(multipart_not_installed_error)
        raise RuntimeError(multipart_not_installed_error) from None

Description

• python-multipart changed its namespace from multipart to python_multipart in version 0.014, hence the package import check fails.
• installing python-mulitpart in version 0.0.12 helps
• It would probably help to either pin the version, or change the import of mulitpart

Operating System

macOS

Operating System Details

Should not matter which system

FastAPI Version

0.115.3

Pydantic Version

2.9.2

Python Version

3.12.6

Additional Context

No response

[saeedghadiri]

I tried using python-multipart==0.0.12 with FastAPI version 0.15.3, and while this prevented the initial error, it resulted in a 400 Bad Request error.

Code to reproduce the issue:

from fastapi import APIRouter, File, UploadFile

router = APIRouter()

@router.post("/short")
async def perform_short(file: UploadFile = File(...)):
    audio_content = await file.read()
    return "ok"

Expected behavior:

The file should upload successfully without errors.

Observed behavior:

• With FastAPI 0.15.3 and python-multipart==0.0.14: The application returns import error for python-multipart.
• With FastAPI 0.15.3 and python-multipart==0.0.12: It returns a 400 Bad Request error.
• With FastAPI 0.15.2: The issue is resolved.

[blueriver97]

I encountered a similar issue with OAuth, and in my case, it worked when I used python-multipart==0.0.13 with FastAPI version 0.115.3.

Although version 0.0.12 is the latest version available on PyPI, for some reason, version 0.0.13 was installed.

• MacOS
• python 3.11.9
• FastAPI 0.115.3

[BobbyTumur]

I just encountered with this issue on AsyncClient with pytest.
pytest kept failing, yelling me to install python-multipart when it's already installed as I checked pip list, the version was 0.0.15.
I tried uninstalling, installing it over and over again which didn't help me but found this link on stackoverflow:

https://stackoverflow.com/questions/76659992/python-fastapi-package-python-multipart-installed-but-not-found

and installed with "pip install python-multipart==0.0.12" which solved the problem.

I am not sure if it's related as I am complete noob, I don't even know what python-multipart does but got my problem fixed, so no complaint.

[odrling]

With the latest python-multipart import multipart should work somehow but from multipart import __version__ doesn’t and causes the current check in FastAPI to fail.

There are two PRs trying to fix this issue currently:
#12607
#12618

[pawelad]

Related issue on the other repo: Kludex/python-multipart#166

[Kludex]

It was an oversight. This was fixed on python-multipart==0.0.16.