Minimal, modern embedded V8 for Python.

py_mini_racer, python, v8-javascript-engine
pip install py-mini-racer==0.6.0


Minimal, modern embedded V8 for Python.



  • Latest ECMAScript support
  • Web Assembly support
  • Unicode support
  • Thread safe
  • Re-usable contexts

MiniRacer can be easily used by Django or Flask projects to minify assets, run babel or WASM modules.


MiniRacer is straightforward to use:

>>> from py_mini_racer import MiniRacer
>>> ctx = MiniRacer()
>>> ctx.eval("1+1")
>>> ctx.eval("var x = {company: 'Sqreen'};")
>>> print(ctx.eval("'\N{HEAVY BLACK HEART}'"))
>>> ctx.eval("var fun = () => ({ foo: 1 });")

Variables are kept inside of a context:

>>> ctx.eval("")

While eval only supports returning primitive data types such as strings, call supports returning composite types such as objects:

{'foo': 1}

Composite values are serialized using JSON. Use a custom JSON encoder when sending non-JSON encodable parameters:

import json

from datetime import datetime

class CustomEncoder(json.JSONEncoder):

        def default(self, obj):
            if isinstance(obj, datetime):
                return obj.isoformat()

            return json.JSONEncoder.default(self, obj)
>>> ctx.eval("var f = function(args) { return args; }")
>>>"f",, encoder=CustomEncoder)

MiniRacer is ES6 capable:

>>> ctx.execute("[1,2,3].includes(5)")

V8 heap information can be retrieved:

>>> ctx.heap_stats()
{'total_physical_size': 1613896,
 'used_heap_size': 1512520,
 'total_heap_size': 3997696,
 'total_heap_size_executable': 3145728,
 'heap_size_limit': 1501560832}

A WASM example is available in the tests.


PyMiniRacer is compatible with Python 2 & 3 and based on ctypes.

The binary builds have been tested on x86_64 with:

  • macOS >= 10.13
  • Ubuntu >= 16.04
  • Debian >= 9
  • CentOS >= 7
  • Alpine >= 3.11
  • Windows 10

It should work on any Linux with a libc >= 2.12 and a wheel compatible pip (>= 8.1).

If you're running Alpine Linux, you may need to install required dependencies manually using the following command:

$ apk add libgcc libstdc++

If you have a up-to-date pip and it doesn't use a wheel, you might have an environment for which no wheel is built. Please open an issue.


We built Python wheels (prebuilt binaries) for macOS 64 bits, Linux 64 bits and Windows 64 bits.

$ pip install py-mini-racer


Warning: building this package from source takes several GB of disk space and takes ~60 minutes.

First check that your current Python executable is version 2.7. This is required by the V8 build system.

$ python --version
Python 2.7.16

You can build the extension with the following command:

$ python helpers/

You can generate a wheel for whatever Python version with the command:

$ python3 helpers/ wheel dist

It will then build V8, the extension, and generates a wheel for your current Python version. The V8 builds are cached in the py_mini_racer/extension/v8/ directory.

Notes for building on macOS

The legacy Python binary builds (OSX 10.6) need to be downloaded from:

They will allow to build a wheel compatible with former OSX versions.


If you want to run the tests, you need to build the extension first, first install pytest:

$ python -m pip install pytest

Then launch:

$ python -m pytest tests


Built with love by Sqreen.

PyMiniRacer launch was described in this blog post.

PyMiniRacer is inspired by mini_racer, built for the Ruby world by Sam Saffron.

Cookiecutter-pypackage was used as this package skeleton.