Repeated <py-env> additions cause steady WebAssembly memory growth in PyScript

Answer

There is no built‑in PyScript API to reset or free the Pyodide interpreter without reloading the page. The only reliable way to reclaim the WebAssembly memory is to ensure no JavaScript reference to the pyodide instance remains, allowing the browser’s garbage collector to free the associated ArrayBuffer.

Explanation

Each <py-env> element creates an independent Pyodide runtime. The runtime owns a WebAssembly Module and its memory buffer (an ArrayBuffer). When the element stays in the DOM, PyScript keeps a reference to the pyodide object, so the buffer is not released. Repeatedly adding new <py-env> tags therefore adds new buffers, and the old ones stay allocated.

Confirmed facts

• Pyodide is compiled to WebAssembly; its memory lives in a JS ArrayBuffer owned by the interpreter object.
• Browsers reclaim that memory only when the interpreter object is garbage‑collected.
• Removing the <py-env> element does not automatically delete the interpreter reference unless PyScript explicitly clears it.

Steps to mitigate

1. Prefer a single <py-env> per page and load additional packages by updating its packages attribute or by using <py-script> that shares the same environment.
2. If you must replace the environment, remove the old element from the DOM and then explicitly delete any stored reference to the pyodide instance (e.g., delete window.myPyodide; or setting the variable to null).
3. After removal, you can optionally trigger a garbage collection in DevTools (window.gc() if the Chrome flag is enabled) to verify that the memory drops.
4. Check whether your PyScript version exposes a dispose() or destroy() method on the pyodide object; if it does, call it after removing the element.

Missing diagnostic detail

Does the version of PyScript you are using provide a public method to release the pyodide instance (e.g., pyodide.dispose())? Knowing this would change the recommendation from relying solely on garbage collection to calling that method directly.