Python in WebAssembly
Python is one of the most popular programming languages in the world, and its WebAssembly implementation seems to be coming along quickly.
Available Implementations
WebAssembly support is officially available in CPython 3.11 and after. The GitHub CPython repo has all of the code.
There is also a Spin SDK for Python that uses CPython, but reduces startup time by preloading and initializing the scripts. There’s a detailed blog post about Python on Fermyon.com that explains this.
Prerequisite
Ensure that you have Python 3.10 or later installed on your system. You can check your Python version by running:
python3 --version
If you do not have Python 3.10 or later, you can install it by following the instructions here.
Usage
The Spin SDK makes it very easy to build Python-based Wasm applications simply by using a Spin template that handles all of the heavy lifting.
Spin’s Python HTTP Request Handler Template
Spin’s Python HTTP Request Handler Template can be installed from spin-python-sdk repository using the following command:
$ spin templates install --git https://github.com/fermyon/spin-python-sdk --update
The above command will install the http-py
template and produce an output similar to the following:
Copying remote template source
Installing template http-py...
Installed 1 template(s)
+---------------------------------------------+
| Name Description |
+=============================================+
| http-py HTTP request handler using Python |
+---------------------------------------------+
Please note: For more information about managing spin templates
, see the templates section in the Spin Command Line Interface (CLI) documentation.
Example
Let’s use Spin’s Python HTTP request handler template, to create a new project:
$ spin new python-example -t http-py --accept-defaults
System Housekeeping (Use a Virtual Environment)
Once the app is created, we can change into the python-example
directory, create and activate a virtual environment and then install the apps requirements:
$ cd python-example
Create a virtual environment directory (we are still inside the Spin app directory):
# python<version> -m venv <virtual-environment-name>
$ python3 -m venv venv-dir
Activate the virtual environment (this command depends on which operating system you are using):
# macOS command to activate
$ source venv-dir/bin/activate
The (venv-dir)
will prefix your terminal prompt now:
(venv-dir) user@123-456-7-8 python-example %
Requirements
The requirements.txt
, by default, contains the references to the spin-sdk
and componentize-py
packages. These can be installed right there in your virtual environment using:
$ pip3 install -r requirements.txt
Take a look at the scaffolded program in app.py
:
from spin_sdk.http import IncomingHandler, Request, Response
class IncomingHandler(IncomingHandler):
def handle_request(self, request: Request) -> Response:
return Response(
200,
{"content-type": "text/plain"},
bytes("Hello from Python!", "utf-8")
)
Change into the app directory and install the requirements:
$ pip3 install -r requirements.txt
Compile a Wasm binary with the scripts preloaded, and then start up a local server:
$ spin build --up
Building component python-example with `componentize-py -w spin-http componentize app -o app.wasm`
Component built successfully
Finished building all Spin components
Logging component stdio to ".spin/logs/"
Preparing Wasm modules is taking a few seconds...
Serving http://127.0.0.1:3000
Available Routes:
python-example: http://127.0.0.1:3000 (wildcard)
Test it with curl
:
$ curl localhost:3000/
Hello from the Python SDK
The file app.wasm
contains both the interpreter (in an initialized state) and all of the userland code:
$ ls -lah app.wasm
-rw-r--r-- 1 technosophos staff 24M Oct 26 18:22 app.wasm
Learn More
Live Code Tuesday Video (Python & Wasm - Let’s talk about componentize-py w/ Joel Dice, Streamed live on Mar 13, 2024)
Joel’s video on Spin, Python, and Components (Recorded at WasmCon on Sep 12, 2023):
Here are some great resources:
- A tutorial for building Python Wasm apps with Spin
- A tutorial doing AI inferencing with Python and Spin
- The Spin Python SDK
- The Spin Developer Docs fully document the Python SDKs
- Python Wasm examples at Spin Up Hub
- The Componentize-Py tooling
- VMware has a distribution of CPython as Wasm based on the official CPython
- A detailed document about the (once) current state and features of Wasm in the latest CPython version (Now outdated)
- Fermyon.com published a slightly more in-depth Python and Wasm tutorial
- An in-browser Python shell in Wasm (Not the preferred path)
- One version of CPython + Wasm, where they are working on WASI support
- SingleStore’s wasi-python project is another approach
Troubleshooting
If you bump into issues when installing the requirements.txt. For example:
error: externally-managed-environment
× This environment is externally managed
Please note, this error is specific to Homebrew-installed Python installations and occurs because installing a non-brew-packaged Python package requires you to either:
- create a virtual environment using
python3 -m venv path/to/venv
, or - use the
--break-system-packages
option in yourpip3 install
command i.e.pip3 install -r requirements.txt --break-system-packages
We recommend installing a virtual environment using venv
, as shown in the system housekeeping section above.