README.md

Embedded Python Interpreter for Go

This library provides an embedded distribution of Python, which should work out-of-the box on a selected set of architectures and operating systems.

This library does not require CGO and solely relies on executing Python inside another process. It does not rely on CPython binding to work. There is also no need to have Python pre-installed on the target host.

You really only have to depend on this library and invoke it as follows:

import (
	"github.com/kluctl/go-embed-python/python"
	"os"
)

func main() {
	ep, err := python.NewEmbeddedPython("example")
	if err != nil {
		panic(err)
	}

	cmd := ep.PythonCmd("-c", "print('hello')")
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	err = cmd.Run()
	if err != nil {
		panic(err)
	}
}

Supported architectures

The following operating systems and architectures are supported:

• darwin-amd64
• darwin-arm64
• linux-amd64
• linux-arm64
• windows-amd64

How it works

This library uses the standalone Python distributions found at https://github.com/indygreg/python-build-standalone as the base.

Running go generate ./... from the root of the project will will trigger download, extraction and cleanup of these distributions for all supported platforms. Cleanup means that everything is removed from the distributions that is not required to run the Python interpreter.

//go:embed is then used to embed the extracted distributions into the compiled go binaries. The EmbeddedPython object is then used as a helper utility to access the embedded distribution.

EmbeddedPython is created via NewEmbeddedPython, which will extract the embedded distribution into a temporary folder. Extraction is optimized in a way that it is only executed when needed (by verifying integrity of previously extracted distributions).

Upgrading python

The Python version and downloaded distributions are controlled via python/internal/generate/main.go. To upgrade Python, increase the version number and re-run go generate ./.... Commit the result to git and then create a release.

Embedding Python libraries into your applications

This library provides utilities/helpers to allow embedding of external libraries into your own application.

To do this, create a simple generator application inside your application/library, for example in internal/my-python-libs/generate/main.go:

package main

import (
	"github.com/kluctl/go-embed-python/pip"
)

func main() {
	err := pip.CreateEmbeddedPipPackagesForKnownPlatforms("requirements.txt", "./data/")
	if err != nil {
		panic(err)
	}
}

Then create add the //go:generate go run ./generate statement to a .go file above the generator source, e.g. in internal/my-python-libs/dummy.go:

package internal

//go:generate go run ./generate

And the requirements.txt in internal/my-python-libs/requirements.txt:

jinja2==3.1.2

When running go generate ./... inside your application/library, you'll get the referenced Python libraries installed to internal/my-python-libs/data. The embedded data is then available via data.Data and can be passed to embed_util.NewEmbeddedFiles() for extraction.

The path returned by EmbeddedFiles.GetExtractedPath() can then be added to the EmbeddedPython by calling AddPythonPath on it.

An example of all this can be found in https://github.com/kluctl/go-jinja2

Why another go+python solution?

There are already multiple implementations of go-bindings for Python, which however all rely on CGO and/or dynamic linking. I experimented a lot with these and was not able to make it stable enough so that I could use it without fear of the process crashing after some time. I even got to the point where I implemented my own dynamic library loader that was not depending on CGO, but ultimately gave up when I realized that it would not work on all platforms.

The only solution that was left was to spawn a Python process and use some kind of inter-process communication. For this to work reliably, without any dependencies on the host system, it was required to embed a fully working Python distribution into my Go binaries. I managed to make this flexible enough to put into a library so that others might benefit as well.

Initially, this approach/code was part of https://github.com/kluctl/kluctl to allow Jinja2 templates in Go. The Jinja2 part can now be found in https://github.com/kluctl/go-jinja2.