WebAssembly#
Limitations#
There is no terminal in WASM. You do have a filesystem, though it is a sandboxed one - you can’t access arbitrary files on a users computer. There is an opt-in experiment for chrome that loads a a directory with user permissions. JuptyerLite keeps its directory in your browser’s cache, so it is persistent.
Sync IO does not work in WASM. This includes time.sleep, which just returns
instantly. Use await asyncio.sleep instead.
Threading is not available (yet?), including multiprocessing, threading, and
sockets. Use async programming instead.
Libraries that draw to the screen (tkinter, turtle, the idle app) or are
highly integrated with the console (curses) are not available. Use HTML or
javascript instead. venv and ensurepip are not available, use micropip
instead.
Furthermore, I’ve found debugging in JupyterLite to not work very well (or at all?), and importing files from the local filesystem may require a little more setup than you are used to.
Installing packages#
Since there’s no terminal, you need to use the micropip library to install
packages. Use it like this, for example to install rich:
import micropip
await micropip.install("rich")
You can install anything that has a pure Python wheel, and has either pure Python wheel dependencies or dependencies already compiled into the Pyodide distribution. Binary packages have to be compiled into Pyodide or compiled separately into WASM and provided by URL - binaries are not get backward compatible enough to be proposed and added to PyPI.
Pyodide compiles many of the most popular data science libraries, like NumPy, Pandas, and more. It even has a patched version of matplotlib.