Unable to see graphviz output from PyMC

[ericmjl]

Describe the bug

When I try to display a PyMC model's graphviz format in Marimo notebooks, nothing shows up:

I am running marimo through uvx. The exact command I used is this:

uvx marimo edit --sandbox notebooks/pymc_demo.py

pymc_demo.py is pasted below.

I am unsure if this is due to a code bug in Marimo or in PyMC. Would love to help out somehow to make it work!

Environment

{
  "marimo": "0.11.25",
  "OS": "Darwin",
  "OS Version": "24.3.0",
  "Processor": "arm",
  "Python Version": "3.13.2",
  "Binaries": {
    "Browser": "--",
    "Node": "--"
  },
  "Dependencies": {
    "click": "8.1.8",
    "docutils": "0.21.2",
    "itsdangerous": "2.2.0",
    "jedi": "0.19.2",
    "markdown": "3.7",
    "narwhals": "1.31.0",
    "packaging": "24.2",
    "psutil": "7.0.0",
    "pygments": "2.19.1",
    "pymdown-extensions": "10.14.3",
    "pyyaml": "6.0.2",
    "ruff": "0.11.2",
    "starlette": "0.46.1",
    "tomlkit": "0.13.2",
    "typing-extensions": "missing",
    "uvicorn": "0.34.0",
    "websockets": "15.0.1"
  },
  "Optional Dependencies": {},
  "Experimental Flags": {
    "rtc": true,
    "chat_sidebar": true,
    "inline_ai_tooltip": true
  }
}

Code to reproduce

# /// script
# requires-python = ">=3.13"
# dependencies = [
#     "graphviz==0.20.3",
#     "marimo",
#     "pymc==5.21.1",
# ]
# ///

import marimo

__generated_with = "0.11.25"
app = marimo.App(width="medium")


@app.cell
def _():
    import pymc as pm
    return (pm,)


@app.cell
def _(pm):
    with pm.Model() as model:
        x = pm.Normal("x", mu=0, sigma=1)
        y = pm.Normal("y", mu=2, sigma=3)
    return model, x, y


@app.cell
def _(model, pm):
    with model:
        trace = pm.sample_prior_predictive()
    return (trace,)


@app.cell
def _(model, pm):
    with model:
        pm.model_to_graphviz()
    return


@app.cell
def _():
    return


if __name__ == "__main__":
    app.run()

[ericmjl]

(In case it's of any encouragement, I've fully recommended marimo notebooks to my teammates as part of a broader toolset upgrade!)

[mscolnick]

@ericmjl

you need to return an expression or variable as the last line, but if-statements or with-blocks won't work.

can you try this code:

with model:
    _out = pm.model_to_graphviz()
_out

[ericmjl]

Thanks for getting back, @mscolnick! It looks like that doesn't work:

As a hint, I tried displaying the return from pm.model_to_graphviz(), and it indeed isn't a NoneType, which is reassuring. Can I ask, what is the requirement for an object to be rendered? Does it have to implement, say, __repr_html__? Or is it something else? (Perhaps I should go read the docs and answer it for myself in parallel!)

[mscolnick]

@ericmjl , there are a few ways to render objects in marimo: https://docs.marimo.io/guides/integrating_with_marimo/displaying_objects/

It looks like it tried to output something, but maybe could not be rendered properly. If it outputs HTML that runs scripts and has lots of globals/styles, it is best to put it in an iframe. mo.iframe(out.to_html())