python.md

Using C7EMR - Python

Status: ✅ loading and running .py files works end-to-end, via Brython.

1. Write your Python

Standard Python 3, as implemented by Brython - including standard library imports (brython_stdlib.js is loaded alongside brython.js). Give your entry file a name, e.g. main.py:

# main.py
print("hello from Python")

Copy it, unmodified, into your mod's ui/ folder.

2. Wire it up in your .modinfo

Don't declare your .py files as <UIScripts>. This mod's loader (C7EMR.loadPython, below) fetches and compiles them itself:

<Dependencies>
    <Mod id="ytm-c7emr-python" title="C7EMR - Python" />
</Dependencies>
...
<ActionGroups>
    <ActionGroup id="your-mod-game" scope="game" criteria="always">
        <Actions>
            <UIScripts>
                <Item>ui/your-mod-entry.js</Item>
            </UIScripts>
            <ImportFiles>
                <Item>ui/main.py</Item>
            </ImportFiles>
        </Actions>
    </ActionGroup>
    <!-- can and/or specify an ActionGroup with scope="shell" -->
</ActionGroups>

3. Write a small entry script

Your entry script is the only file declared as <UIScripts>. It waits for C7EMR.loadPython to exist, then hands it the path to your .py file:

(function waitForC7emr() {
    if (typeof C7EMR === 'undefined' || typeof C7EMR.loadPython !== 'function') {
        setTimeout(waitForC7emr, 10);
        return;
    }
    C7EMR.loadPython('<your-mod-id>/ui/main.py').catch(function (err) {
        console.error('loadPython failed:', err);
    });
})();

The first call to C7EMR.loadPython also lazily loads brython.js and brython_stdlib.js (once, shared across all mods depending on this one) before running your script.

Errors

Brython prints a full Python traceback to the console itself whenever a loaded script raises an uncaught exception (syntax errors included). C7EMR.loadPython's returned promise also rejects, but only with a short one-line summary - treat the console as the source of truth for debugging, not the caught JS error.

Sharing state across multiple loadPython calls

Every C7EMR.loadPython call runs against the same Brython VM, so top-level names set by one script are visible to scripts loaded afterwards - useful for splitting a mod into multiple .py files that share state.

Calling into JS from Python

Use Brython's built-in browser package, e.g. from browser import window.