componentize-py

A Bytecode Alliance project

This is a tool to convert a Python application to a WebAssembly component. It takes the following as input:

• a WIT file or directory
• the name of a WIT world defined in the above file or directory
• the name of a Python module which targets said world
• a list of directories in which to find the Python module and its dependencies

The output is a component which may be run using e.g. wasmtime.

Getting Started

First, install Python 3.10 or later and pip if you don't already have them. Then, install componentize-py:

pip install componentize-py

Next, create or download the WIT world you'd like to target, e.g.:

cat >hello.wit <<EOF
package example:hello;
world hello {
  export hello: func() -> string;
}
EOF

If you're using an IDE or just want to examine the bindings produced for the WIT world, you can generate them using the bindings subcommand:

componentize-py -d hello.wit -w hello bindings hello_guest

Then, use the hello module produced by the command above to write your app:

cat >app.py <<EOF
import wit_world
class WitWorld(wit_world.WitWorld):
    def hello(self) -> str:
        return "Hello, World!"
EOF

And finally generate the component:

componentize-py -d hello.wit -w hello componentize --stub-wasi app -o app.wasm

To test it, you can install wasmtime-py and use it to generate host-side bindings for the component:

[!NOTE] Due to compatibility issues with wasmtime-py versions beyond 38.x, this example requires version 38.0.0 or earlier: pip install "wasmtime==38.0.0"

pip install wasmtime
python3 -m wasmtime.bindgen app.wasm --out-dir hello_host

Now we can write a simple host app using those bindings:

cat >host.py <<EOF
from hello_host import Root
from wasmtime import Config, Engine, Store

config = Config()
config.cache = True
engine = Engine(config)
store = Store(engine)
hello = Root(store)
print(f"component says: {hello.hello(store)}")
EOF

And finally run it:

 $ python3 host.py
component says: Hello, World!

See the examples directories for more examples, including various ways to run the components you've created.

Known Limitations

Currently, the application can only import dependencies during build time, which means any imports used at runtime must be resolved at the top level of the application module. For example, if x is a module with a submodule named y the following may not work:

import x

class Hello(hello.Hello):
    def hello(self) -> str:
        return x.y.foo()

That's because importing x does not necessarily resolve y. This can be addressed by modifying the code to import y at the top level of the file:

from x import y

class Hello(hello.Hello):
    def hello(self) -> str:
        return y.foo()

This limitation is being tracked as issue #23.

See the issue tracker for other known issues.

Contributing

See CONTRIBUTING.md for details on how to contribute to the project and build it from source.