To install wasmtime-py, run this command in your terminal:

$ pip install wasmtime

The package currently supports 64-bit builds of Python 3.9+ on Windows, macOS, and Linux, for x86_64 and arm64 architectures.

wasmtime-py follows the Wasmtime versioning scheme, with a new major version being released every month. As with Wasmtime itself, new major versions of wasmtime-py can contain changes that break code written against the previous major version.

Since every installed Python package needs to agree on a single version of wasmtime-py, to use the upper bound on the major version in the dependency requirement should be bumped reguarly, ideally as soon as a new wasmtime-py version is released. To automate this process it is possible to use the whitequark/track-pypi-dependency-version script. YoWASP/runtime is an example of a project that automatically publishes releases on PyPI once a new version of wasmtime-py is released if it passes the testsuite.

In this example, we compile and instantiate a WebAssembly module and use it from Python:

from wasmtime import Store, Module, Instance, Func, FuncType
store = Store()
module = Module(store.engine, """
  (module
    (func $hello (import "" "hello"))
    (func (export "run") (call $hello))
  )
""")
def say_hello():
    print("Hello from Python!")
hello = Func(store, FuncType([], []), say_hello)
instance = Instance(store, module, [hello])
run = instance.exports(store)["run"]
run(store)

Be sure to check out the examples directory, which has other usage patterns as well as the full API documentation of the wasmtime-py package.

If your WebAssembly module works this way, then you can also import the WebAssembly module directly into Python without explicitly compiling and instantiating it yourself:

# Import the custom loader for `*.wasm` files
import wasmtime.loader
# Assuming `your_wasm_file.wasm` is in the python load path...
import your_wasm_file
# Now you're compiled and instantiated and ready to go!
print(your_wasm_file.run())

Components are also supported in wasmtime-py. For more information see the documentation of wasmtime.component. Using a component is similar to using core wasm modules, and for examples see the tests/component/ directory.

See CONTRIBUTING.md.