pyodide/docs/usage/wasm-constraints.md

# Pyodide Python compatibility

## Python Standard library

Most of the Python standard library is functional, except for the modules
listed in the sections below. A large part of the CPython test suite passes except for
tests skipped in
[`src/tests/python_tests.yaml`](https://github.com/pyodide/pyodide/blob/main/src/tests/python_tests.yaml)
or via [patches](https://github.com/pyodide/pyodide/tree/main/cpython/patches).

### Optional modules

The following stdlib modules are unvendored by default,
in order to reduce initial download size of Python distribution.
You can load all unvendored stdlib modules
when initializing Pyodide with, `loadPyodide({ fullStdLib : true })`.
However this has a significant impact on the download size.
Instead, it is better to load individual modules as needed using
{any}`pyodide.loadPackage` or {any}`micropip.install`.

- distutils
- ssl
- lzma
- sqlite3
- test: it is an exception to the above, since it is not loaded even if `fullStdLib` is set to true.

### Removed modules

The following modules are removed from the standard library to reduce download size and
since they currently wouldn't work in the WebAssembly VM,

- curses
- dbm
- ensurepip
- idlelib
- lib2to3
- tkinter
- turtle.py
- turtledemo
- venv
- pwd

### Included but not working modules

The following modules can be imported, but are not functional due to the limitations of the WebAssembly VM:

- multiprocessing
- threading
- sockets

as well as any functionality that requires these.