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MW003: incompatible-package

🌐 WASM ❌ Not Fixable

MW003: Packages in the dependency tree incompatible with WASM.

What it does

Reads the notebook's PEP 723 dependencies, filters out requirements whose PEP 508 markers exclude Emscripten (for example torch; sys_platform != 'emscripten'), walks their transitive dependency tree via installed metadata, then queries PyPI's JSON API to check whether each package has a py3-none-any, emscripten, or wasm32 wheel available. Packages only in pyodide-lock.json are also accepted.

For a package that Pyodide ships, the version in pyodide-lock.json is the only version the browser can install. If the notebook's specifier excludes that version, the rule reports the mismatch.

Why is this bad?

Pyodide can only install pure-Python wheels via micropip, or packages that are pre-built in the Pyodide distribution. Packages with only platform-specific native wheels will fail to install in the browser.

A specifier that excludes the Pyodide build cannot be honored there. marimo export html-wasm rewrites it to the lockfile version, so the pin in the source notebook is misleading; in the browser without that rewrite, micropip rejects the whole install, including every other dependency listed alongside it.

Examples

Problematic: 

import jax  # jaxlib (transitive dep) has only native wheels

Problematic: 

# /// script
# dependencies = ["numpy==1.26.0"]  # Pyodide ships numpy 2.4.3
# ///

Not flagged: 

import numpy  # Native, but pre-built in Pyodide

Not flagged: 

import requests  # Pure Python wheel on PyPI

Not flagged (PEP 723 metadata): 

# /// script
# dependencies = ["jax; sys_platform != 'emscripten'"]
# ///
# jax is excluded from WASM checks via PEP 508 marker

References