Limitations of the "file" protocol

Frequently asked questions

Syntax, keywords and built-in functions

Standard distribution

import implementation

Brython packages

Browser interface

Introduction - DOM API
Creating a document
Accessing elements
Attributes, properties and methods

Mouse events
Keyboard events
Focus events
Drag events

Query string

Using Javascript objects and libraries

Brython-specific built-in modules




Working with Brython

Options of function brython()
Testing and debugging
Deploying an application


Hello world !
Insert content in an element
HTML markup (bold,italic...)
HTML table
Bind and unbind events
Handle options in a SELECT
Drag and drop
Get the content of an element
Read the content of a file
Store objects locally
Example of onmouseover

Using Javascript objects

We have to handle the transition period when Brython is going to coexist with Javascript ;-)

Accessing Brython objects from Javascript

By default, Brython only exposes two names in the global Javascript namespace:

brython() : the function run on page load

__BRYTHON__ : an object used internally by Brython to store the objects needed for scripts execution

Consequently, by default, a Javascript program cannot access Brython objects. For instance, for a function echo() defined in a Brython script to react to an event on an element in the page, instead of using the regular javascript syntax:

<button onclick="echo()">

(because the brython function echo is not accessible from Javascript), the solution is to set an id to the element:

<button id="mybutton">

and to define the link between this element and the event click by :

from browser import document
document['mybutton'].bind('click', echo)

Another option is to force the introduction of the name echo in the Javascript namespace, by defining it as an attribute of the object window in module browser :

from browser import window
window.echo = echo

NOTE: This method is not recommended, because it introduces a risk of conflict with names defined in a Javascript program or library used in the page.

Objects in Javascript programs

An HTML document can use Javascript scripts or libraries, and Python scripts or libraries

The names added by Javascript programs to the global Javascript namespace are available in Brython scripts as attributes of the object window defined in the module browser

For instance :

<script type="text/javascript">
circle = {surface: function(r){return 3.14 * r * r}}

<script type="text/python">
from browser import document, window

document['result'].value =

Javascript objects are converted into their Python equivalent in this way :

Javascript object (js_obj)Python object (window.js_obj)
DOM elementinstance of DOMNode
DOM eventinstance of DOMEvent
Collection of DOM elementslist of DOMNode instances
true, falseTrue, False
nullunchanged (printed as '')
Integerinstance of int
Floatinstance of float
Stringinstance of str
Arrayinstance of list

The other Javascript objects are converted into an instance of the class JSObject defined in module javascript. They can be converted into a Python dictionary by :

py_obj = window.js_obj.to_dict()

If the Javascript object is a function, the arguments passed to the Python function are converted into Javascript objects, using the reverse of the above table. If the argument is a Python dictionary, it is converted into a Javascript object; keys in the Python dictionary are converted to strings in the Javascript object.

Take care, a Javascript function can't be called with keyword arguments, this raises a TypeError exception : if the function is defined by

function foo(x, y)

and if it is called from a Brython script by, x=1)

passing the arguments in the expected order is not possible, because the Brython script doesn't know the signature of the Javascript function.

Using Javascript constructors

If a Javascript function is an object constructor, that can be called in Javascript code with the keyword new, it can be used in Brython using the new special method added by Brython to the Javascript object.

For instance :

<script type="text/javascript">
function Rectangle(x0, y0, x1, y1){
    this.x0 = x0
    this.y0 = y0
    this.x1 = x1
    this.y1 = y1
    this.surface = function(){return (x1 - x0) * (y1 - y0)}

<script type="text/python">
from browser import alert, window

rectangle = window.Rectangle
alert(, 10, 30, 30).surface())

jQuery example

Here is a more complete example of how you can use the popular library jQuery:

<script src="//">
<script src="/src/brython.js"></script>

<script type="text/python">
from browser import window

jq = window.jQuery

# Ajax call
def onSuccess(data, status, req):

        {'foo': 56},
     'success': onSuccess

# add an option to a SELECT box
jq('#sel').append('<' + 'option>three')

# access element attributes
assert jq('#c').attr('id') == 'c'

# define a callback for a click on a button
def callback(ev):

jq('#btn').on('click', callback)

# we can even use "each" to iterate on SPAN elements
def show(i, obj):
    print(i, obj)

jq.each(jq('span'), show)

<body onload="brython(1)">

<select id="sel">
  <option value="one">one
  <option value="two">two

<span id="c"></span>

<button id="btn">click</button>


Other examples

You will find in the gallery other examples of how to use Javascript libraries (Three, Highcharts, Raphael) in Brython scripts.

Integration of a Javascript library in a Python module

Another way to integrate a library is to create a Python module than can be imported in scripts, without having to load this library in the script page.

For that, the library must be accessible through an Ajax call? It is loaded by the function load(url) of the browser module, and the names that it adds to the global Javascript namespace are exposed in the Python module.

For instance, we can create a module jquery:

from browser import window, load


# jQuery adds the name jQuery to the global Javascript namespace
# (also called $, but this is not a valid Python identifier)
jq = window.jQuery

We can then use this module in a Brython page (notice that we don't load jquery.js):

<script src="brython.js"></script>
<body onload="brython(1)">
<script type="text/python">
import jquery

jquery("#test").text("I can use jQuery here !")

<div id="test"></div>