Python Tooling

Building a Component with componentize-py

componentize-py is a tool that converts a Python application to a WebAssembly component.

Create a Python program that implements the add function in the example world. Note that it imports the bindings that will be created by componentize-py:

$ cat<<EOT >>
import example

class Example(example.Example):
    def add(x: int, y: int) -> int:
        return x + y

Install componentize-py and generate a component from

$ pip install componentize-py
$ componentize-py -d /path/to/examples/example-host/add.wit -w example componentize guest -o add.wasm
Component built successfully

To test the component, run it using the Rust add host:

$ cd component-model/examples/add-host
$ cargo run --release -- 1 2 ../path/to/add.wasm
1 + 2 = 3

Running components from Python Applications

Wasm components can also be invoked from Python applications. This walks through the tooling needed to call the app.wasm component from the previous section from a Python application. First, install wasmtime-py, being sure to use a version this PR has merged or working off that branch.

Note: be sure to use at least Python 3.11

$ git clone
$ (cd wasmtime-py && python ci/ && python ci/ && pip install .)

Now, generate the bindings to be able to call the component from a Python host application.

$ python3 -m wasmtime.bindgen add.wasm --out-dir add

The generated package add has all of the requisite exports/imports for the component and is annotated with types to assist with type-checking and self-documentation as much as possible.

Now, create a Python program to run the component. Note that imports for WASI preview 2 are explicitly set to null. This is because when creating a component from a Python module, componentize-py pulls in extra WASI Preview 2 imports, even if they are not used by the component. Currently, language toolchains are likely to pull in more than a component declares in WAT.

from add import Root, RootImports
from wasmtime import Store

def main():
    store = Store()
    component = Root(store, RootImports(poll=None, monotonic_clock=None, wall_clock=None, streams=None, filesystem=None, random=None, environment=None, preopens=None, exit=None, stdin=None, stdout=None, stderr=None))
    print("1 + 2 = ", component.add(store, 1, 2))

if __name__ == '__main__':

Run the Python host program:

$ python3
1 + 2 = 3