Embed the Duktape JS interpreter in Python

Introduction

Pyduktape is a python wrapper around Duktape, an embeddable Javascript interpreter.

On top of the interpreter wrapper, pyduktape offers easy integration between the Python and the Javascript environments. You can pass Python objects to Javascript, call methods on them and access their attributes. Similarly, you can pass Javascript objects to Python.

Objects are never copied or serialized. Instead, they are passed between the two environments using proxy objects. Proxy objects delegate the execution to the original object environment.

Threading

It is possible to invoke Javascript code from multiple threads. Each thread will need to use its own embedded interpreter. Javascript objects returned to the Python environment will only be usable on the same thread that created them. The runtime always checks this condition automatically, and raises a DuktapeThreadError if it's violated.

Getting Started

Installation

To install from pypi:

$ pip install -U setuptools
$ pip install pyduktape

To install the latest version from github:

$ git clone https://github.com/stefano/pyduktape.git
$ cd pyduktape
$ pip install -U setuptools
$ python setup.py install

Running Javascript code

To run Javascript code, you need to create an execution context and use the method eval_js:

import pyduktape

context = pyduktape.DuktapeContext()
context.eval_js("print('Hello, world!');")

Each execution context starts its own interpreter. Each context is independent, and tied to the Python thread that created it. Memory is automatically managed.

To evaluate external Javascript files, use eval_js_file:

// helloWorld.js
print('Hello, World!');

# in the Python interpreter
import pyduktape

context = pyduktape.DuktapeContext()
context.eval_js_file('helloWorld.js')

Pyduktape supports Javascript modules:

// js/helloWorld.js
exports.sayHello = function () {
    print('Hello, World!');
};

// js/main.js
var helloWorld = require('js/helloWorld');
helloWorld.sayHello();

# in the Python interpreter
import pyduktape

context = pyduktape.DuktapeContext()
context.eval_js_file('js/main')

The .js extension is automatically added if missing. Relative paths are relative to the current working directory, but you can change the base path using set_base_path:

# js/helloWorld.js
print('Hello, World!');

# in the Python interpreter
import pyduktape

context = pyduktape.DuktapeContext()
context.set_base_path('js')
context.eval_js_file('helloWorld')

Python and Javascript integration

You can use set_globals to set Javascript global variables:

import pyduktape

def say_hello(to):
    print 'Hello, {}!'.format(to)

context = pyduktape.DuktapeContext()
context.set_globals(sayHello=say_hello, world='World')
context.eval_js("sayHello(world);")

You can use get_global to access Javascript global variables:

import pyduktape

context = pyduktape.DuktapeContext()
context.eval_js("var helloWorld = 'Hello, World!';")
print context.get_global('helloWorld')

eval_js returns the value of the last expression:

import pyduktape

context = pyduktape.DuktapeContext()
hello_world = context.eval_js("var helloWorld = 'Hello, World!'; helloWorld")
print hello_world

You can seamlessly use Python objects and functions within Javascript code. There are some limitations, though: any Python callable can only be used as a function, and other attributes cannot be accessed. Primitive types (int, float, string, None) are converted to equivalent Javascript primitives. The following code shows how to interact with a Python object from Javascript:

import pyduktape

class Hello(object):
    def __init__(self, what):
        self.what = what

    def say(self):
        print 'Hello, {}!'.format(self.what)

context = pyduktape.DuktapeContext()
context.set_globals(Hello=Hello)
context.eval_js("var helloWorld = Hello('World'); helloWorld.say();")

In the same way, you can use Javascript objects in Python. You can use the special method new to instantiate an object:

import pyduktape

context = pyduktape.DuktapeContext()
Hello = context.eval_js("""
function Hello(what) {
    this.what = what;
}

Hello.prototype.say = function () {
    print('Hello, ' + this.what + '!');
};

Hello
""")

hello_world = Hello.new('World')
hello_world.say()

You can use Python lists and dicts from Javascript, and viceversa:

import pyduktape

context = pyduktape.DuktapeContext()
res = context.eval_js('[1, 2, 3]')

for item in res:
    print item

context.set_globals(lst=[4, 5, 6])
context.eval_js('for (var i = 0; i < lst.length; i++) { print(lst[i]); }')

res = context.eval_js('var x = {a: 1, b: 2}; x')
for key, val in res.items():
    print key, '=', val
res.c = 3
context.eval_js('print(x.c);')

context.set_globals(x=dict(a=1, b=2))
context.eval_js("""
var items = x.items();
for (var i = 0; i < items.length; i++) {
    print(items[i][0] + ' = ' + items[i][1]);
}
""")
context.set_globals(x=dict(a=1, b=2))
context.eval_js('for (var k in x) { print(k + ' = ' + x[k]); }')