pyjamas

build

AJAX apps in Python (like Google did for Java)

Getting Started with

pyjamas

Programming with pyjamas needs a little bit of rethinking about

the way that you do Web application development. Primarily,

you need to forget virtually everything you've ever learned and

come to expect Web development to be. The reason for this is

very simple: Pyjamas is pure javascript. Although written

in python, not javascript, it is essential to bear in mind

that virtually 100% of your web application will be javascript -

not HTML. The programming style you may be accustomed to for

HTML programming involves placing as much HTML into one page

as you can stand, and making the minimum number of exceptions

and allowances for dynamic content that you can manage, without

making the HTML page "too complicated" to be readable.

Pyjamas makes it possible for you to break pages down into concepts.

classes. widgets. maybe some CSS styling is added, almost as an

afterthought, on top of the "real" functionality. In other words, Pyjamas

is actually more like Desktop application development than it is

Web development.

With that in mind, the best possible starting point has to be the

, most of which were ported from

Google Web Toolkit. They will make it really clear just how "not"

Web that pyjamas - and incidentally GWT - really are.

Examples

The simplest example is of course the traditional

or, in this case, Hello AJAX. If you've downloaded pyjamas, you

will be able to browse, with your browser, to the examples directory

and see this in action for yourself. Type

"file://home/yourusername/pyjamas/examples" into your URL bar - or

wherever you have unpacked pyjamas to and continue to browse to

the helloworld output directory.

Once you have played with the example, online, try it on your local

machine. Remember to run the "build.sh" script (if you have linux

or MacOS, or execute python.exe ../../build/build.py Hello.py if

you have windows). Then, take a look at the source code

that generated it, which is shown here:

from pyjamas import Windowfrom pyjamas.ui import RootPanel, Buttondef greet(sender):    Window.alert("Hello, AJAX!")b = Button("Click me", greet)RootPanel().add(b)

The most important thing to note is that everything gets added to

RootPanel. RootPanel() gives you access to the Browser's

DOM model (starting of course at body). To illustrate,

try adding this, and see what happens:

RootPanel().add(HTML("Hello World"))

You should get nothing - and if you look in your Javascript

console for an error message, you should find an error indicating

that "HTML" does not exist. This is correct - because you needed to

add this to the top of the module, along with the other imports:

from pyjamas.ui import HTML

Now if you re-run build.sh, you should see both a button and next

to it the words "Hello World". Congratulations, you've just

successfully developed your first pyjamas application.