Using WebAssembly with Python

Using WebAssembly with Python

Learn how to use WebAssembly (Wasm) with Python

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WebAssembly (often abbreviated as Wasm) is an open standard and low-level binary instruction format designed to execute code on the web. It serves as a portable compilation target for high-level languages like C, C++, Rust, and many others, enabling developers to run computationally intensive applications on the web platform with near-native performance.

Unlike traditional web technologies like JavaScript, WebAssembly is not a programming language but rather a binary format that represents code in a compact and efficient manner. It defines a stack-based virtual machine that executes the instructions directly, offering a fast and predictable runtime environment. WebAssembly modules are typically compiled from higher-level languages into the binary format, making them more compact and efficient compared to equivalent JavaScript code. The binary format is designed to be fast to decode, optimizing load times and allowing for quick startup of applications.

Here's a simple example of using WebAssembly (Wasm) with Python.

Create a simple Wasm module using a language like C or Rust. For this example, let's use a C program that calculates the square of a number:

// square.c

int square(int num) {
    return num * num;

Compile the C code into a Wasm module using Emscripten or another suitable compiler:

emcc square.c -o square.wasm

Now, let's use Python to load and run the Wasm module. Install the wasmtime Python package, which provides a runtime for executing Wasm modules:

pip install wasmtime

Write a Python script that loads and executes the Wasm module:


import wasmtime

# Load the Wasm module
wasm_module = wasmtime.Module.from_file("square.wasm")

# Create an instance of the module
instance = wasmtime.Instance(wasm_module)

# Get a reference to the exported function
square_func = instance.exports.square

# Call the function and print the result
result = square_func(5)
print("Square of 5:", result)

Run the Python script to see the output:


The output will be:

Square of 5: 25

In this example, we compiled a C program into a Wasm module and used the wasmtime Python package to load and execute the module. This demonstrates the integration of Wasm with Python, allowing you to leverage the capabilities of other programming languages within your Python applications.

Containerising Wasm + Python

To containerize the Wasm + Python example, we can use Docker. Here's how you can create a Dockerfile to package the application:

Create a file named Dockerfile (without any file extension) in the same directory as your Python script and Wasm module.

Open the Dockerfile and add the following content:

# Use a Python base image
FROM python:3.9

# Set the working directory inside the container

# Copy the Python script and Wasm module into the container
COPY square.wasm ./

# Install the required Python packages
RUN pip install wasmtime

# Run the Python script
CMD ["python", ""]

Save the Dockerfile.

Open a terminal or command prompt, navigate to the directory containing the Dockerfile and other files, and build the Docker image:

docker build -t wasm-python-example .

After the image is built successfully, you can run a container based on the image:

docker run wasm-python-example

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