Error using system libraries #4

rroblf01 · 2026-01-30T11:25:23Z

rroblf01
Jan 30, 2026

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 the FastAPI Cloud documentation, with the integrated search.
I already searched in Google "How to X in FastAPI Cloud" and didn't find any information.
I already read and followed all the tutorial in the docs and didn't find an answer.
I already checked if it is not related to FastAPI Cloud but to FastAPI.

Example Code

# /// script
# requires-python = ">=3.14"
# dependencies = [
#   "fastapi[standard]==0.128.0",
#   "weasyprint==68.0",
# ]
# ///

from fastapi import FastAPI, Response
from weasyprint import HTML, CSS

app = FastAPI()


@app.get("/")
def main():
    css = CSS(
        string="""
        @page { size: A4; margin: 1cm }
        body { font-family: Arial, sans-serif; }
    """
    )
    html_content = """
    <html>
        <head><title>Sample PDF</title></head>
        <body>
            <h1>Hello, World!</h1>
            <p>This is a sample PDF generated using WeasyPrint.</p>
        </body>
    </html>
    """
    pdf = HTML(string=html_content).write_pdf(stylesheets=[css])
    return Response(content=pdf, media_type="application/pdf")


if __name__ == "__main__":
    import uvicorn

    uvicorn.run(app, host="0.0.0.0", port=8000)

Description

This project (without the __name__ == "__main__" part) can be deployed successfully on FastAPI Cloud, but the problem is that FastAPI Cloud doesn't allow the use of system libraries, so you get this error:

[Jan 30 12:20:34] OSError: cannot load library 'libgobject-2.0-0': libgobject-2.0-0: cannot open
[Jan 30 12:20:34] shared object file: No such file or directory. Additionally,
[Jan 30 12:20:34] ctypes.util.find_library() did not manage to locate a library called
[Jan 30 12:20:34] 'libgobject-2.0-0'

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.128.0

Pydantic Version

2.12.5

FastAPI CLI Version

FastAPI CLI version: 0.0.20

Python Version

Python 3.14.0

Additional Context

No response

tiangolo · 2026-02-17T07:46:48Z

tiangolo
Feb 17, 2026
Maintainer

Thanks for the report! We support some common system libraries but not yet this one.

We are evaluating what to do in this case, it seems this library might be heavyweight, used for the UI in Linux, and we are also considering what would happen if there are version mismatches, etc.

We have this tracked internally to consider what would be the best way to do it. We'll also consider if there could be any alternatives as well that could work better.

1 reply

DoctorJohn Feb 19, 2026
Maintainer

Hey @rroblf01, as mentioned, we're still working on a scalable solution internally.
For now, you could ship the missing shared object files yourself and add them to your PATH by setting an environment variable.

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Error using system libraries #4

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rroblf01 Jan 30, 2026

First Check

Example Code

Description

Operating System

Operating System Details

FastAPI Version

Pydantic Version

FastAPI CLI Version

Python Version

Additional Context

Replies: 1 comment · 1 reply

Uh oh!

tiangolo Feb 17, 2026 Maintainer

Uh oh!

DoctorJohn Feb 19, 2026 Maintainer

rroblf01
Jan 30, 2026

Replies: 1 comment 1 reply

tiangolo
Feb 17, 2026
Maintainer

DoctorJohn Feb 19, 2026
Maintainer