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Python Mini Racer

Minimal, modern embedded V8 for Python.

  • Free software: ISC license



  • Unicode support
  • Thread safe
  • Re-usable contexts
  • Binary object is Python agnostic

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


py_mini_racer is straightforward to use:

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

Variables are kept inside of a context:

>>> ctx.eval("")

You can give directly 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)

PyMiniRacer is ES6 capable:

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

V8 heap information can be retrieved:

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


PyMiniRacer is compatible with Python 2 and Python 3. Wheels are generated for python 2.7 and python 3.4 to python 3.8.

Binary builds availability

The PyMiniRacer binary builds have been tested on x86_64 with:

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

You need pip >= 8.1 to install the wheels - you can check and upgrade yours in this way:

$ pip --version
$ pip install --upgrade pip

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. You need pip >= 1.4 and setuptools >= 0.8.

$ pip install py-mini-racer


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.

Tools used in rendering this package:

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