PyScript Next Runtime Switch Between Pyodide and MicroPython Leads to Unclear Global State Synchronization

Runtime State Isolation

No, re-initializing the PyScript runtime with a different engine does not preserve previously defined Python globals. Pyodide and MicroPython are entirely separate interpreter instances with their own memory heaps, module tables, and global namespaces. Switching from one to the other—or even re-initializing the same engine—effectively starts the new interpreter with a clean slate.

Explanation of Engine Architecture

The lack of synchronization is due to the fundamental difference in how these engines are implemented:

• Pyodide: A full CPython distribution compiled to WebAssembly.
• MicroPython: A lean, optimized implementation designed for constrained environments.

Because these are distinct Wasm modules, there is no shared Python-level memory. Variables, imported modules, or modifications to built-ins created in a MicroPython session are invisible to a subsequent Pyodide session.

How to Synchronize State Across Runtimes

To guarantee that state is shared across runtime switches, you must move the "source of truth" out of the Python interpreter and into the JavaScript host environment. Both engines can interface with the browser's global scope.

1. Use the JS Global Scope: Store shared data in window or a dedicated JavaScript object.
2. Access via the js module: Use the js module available in both runtimes to read and write these values.
3. Serialize Complex Data: Since JS and Python have different type systems, use JSON for complex structures to ensure consistency.

# Example: Writing state in MicroPython
import js
js.window.shared_state = "Active"

# Example: Reading state in Pyodide
import js
print(js.window.shared_state) # Output: Active

Verification Steps

To verify isolation in your specific PyScript version, perform the following test:

• Define a variable (e.g., TEST_VAR = 100) in a MicroPython script.
• Trigger a runtime switch to Pyodide.
• Attempt to print TEST_VAR. A NameError confirms that the namespaces are isolated.

Diagnostic Detail Required: Please specify the exact PyScript version you are using. While the separate-instance behavior is standard, specific lifecycle hooks for runtime disposal vary between releases.