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Minimal, modern embedded V8 for Python.

Project description

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 3.6.

Binary builds availability

The PyMiniRacer binary builds have been tested on x86_64 with:

  • OSX 10.10
  • Ubuntu >= 12.04
  • Debian >= 7
  • CentOS >= 6

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 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 OSX 64 bits and Linux 64 bits - most recent distributions. You need pip >= 1.4 and setuptools >= 0.8.

$ pip install py-mini-racer


You can build v8 with the command:

$ python build_v8

You can also build the ctype extension:

$ python build_ext

Which automatically builds v8.

You can generate a wheel with the command:

$ python bdist_wheel

which builds v8, the extension, and generates a wheel.

Notes for building on OSX

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 V8 first, then launch:

$ python test --addopts 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:


Export V8 version. Fix circular structures export.



0.1.13 (2018-03-15)

  • Add heap_stats function
  • Fix issue with returned strings containing null bytes

0.1.12 (2018-17-04)

  • Remove dependency to enum

0.1.11 (2017-07-11)

  • Add compatibility for centos6

0.1.10 (2017-03-31)

  • Add the possibility to pass a custom JSON encoder in call.

0.1.9 (2017-03-24)

  • Fix the compilation for Ubuntu 12.04 and glibc < 2.17.

0.1.8 (2017-03-02)

  • Update targets build for better compatibility with old Mac OS X and linux platforms.

0.1.7 (2016-10-04)

  • Improve general performances of the JS execution.
  • Add the possibility to build a different version of V8 (for example with debug symbols).
  • Fix a conflict that could happens between statically linked libraries and dynamic ones.

0.1.6 (2016-08-12)

  • Add error message when py_mini_racer sdist fails to build asking to update pip in order to download the pre-compiled wheel instead of the source distribution.

0.1.5 (2016-08-04)

  • Build py_mini_racer against a static Python. When built against a shared library python, it doesn’t work with a static Python.

0.1.4 (2016-08-04)

  • Ensure JSEvalException message is converted to unicode

0.1.3 (2016-08-04)

  • Fix extension loading for python3
  • Add a make target for building distributions (sdist + wheels)
  • Fix eval conversion for python 3

0.1.2 (2016-08-03)

  • Fix date support
  • Fix Dockerfile for generating python3 wheels

0.1.1 (2016-08-02)

  • Fix sdist distribution.

0.1.0 (2016-08-01)

  • First release on PyPI.

Project details

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