Mule 3.4 - scripting in Python

I'm having quite a bit of trouble getting started with scripting in Mule. To be quite honest, I'm falling at the first hurdle - I can't find anything in the documentation which tells me how to access the payload or how to return data to my flow.

I'm using Jython 2.5 and Mule 3.4.

My flow is extremely simple: it takes some text from an Ajax source and simply echoes it. At the moment the Python script does nothing (as I cannot figure out how to get it to do something with the payload).

<flow name="Python Script" doc:name="Python Script">
    <ajax:connector name="connector-ajax" serverUrl="http://192.168.0.1:8000" resourceBase="C:\mule\workspace\scripting\src\main\app\docroot" doc:name="Ajax" />
    <scripting:component doc:name="Python">
        <scripting:script engine="jython" file="C:\mule\workspace\scripting\src\main\app\python\myscript.py"/>
    </scripting:component>
    <echo-component doc:name="Echo"/>
</flow>

I have read through the Script Component Reference and the Scripting Module Reference - the module reference appears to have some relevant information but I can't figure out how to use it in Python.

I have also read through an article about 'Mule Punching' which seems like it would have answered my question if I was running version 2 of Mule. I attempted to use the same techniques in my Mule 3 project but it did not work.

Edit 24/07/2012

Using @ppiixx's response, I have got a little bit further with Python scripting.

Just having a single line of code, for example return len(payload) causes the Jython interpreter to throw an error as return cannot exist outside of a function. Fair enough, that's standard.

However, with the code

def main():
  return len(payload)

main()

I get an error saying that 'No serializer can be found for class org.mule.transport.NullPayload'.

The log is below:

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Started app 'python-test'                                +
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
INFO  2013-07-24 09:16:08,821 [[python-test].flow.stage1.02] org.mule.component.simple.LogComponent: 
********************************************************************************
* Message received in service: flow. Content is: '{NullPayload}'               *
********************************************************************************
ERROR 2013-07-24 09:16:08,849 [[python-test].flow.stage1.02] org.mule.exception.CatchMessagingExceptionStrategy: 
********************************************************************************
Message               : No serializer found for class org.mule.transport.NullPayload and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) ) (org.codehaus.jackson.map.JsonMappingException)
Code                  : MULE_ERROR--2
--------------------------------------------------------------------------------
Exception stack is:
1. No serializer found for class org.mule.transport.NullPayload and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) ) (org.codehaus.jackson.map.JsonMappingException)
  org.codehaus.jackson.map.ser.impl.UnknownSerializer:52 (null)
2. No serializer found for class org.mule.transport.NullPayload and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) ) (org.codehaus.jackson.map.JsonMappingException) (org.mule.api.transformer.TransformerException)
  org.mule.module.json.transformers.ObjectToJson:107 (http://www.mulesoft.org/docs/site/current3/apidocs/org/mule/api/transformer/TransformerException.html)

This leads me to think that using return on its own isn't enough to return data to the flow.

I've read through the scripting module reference, and while it gives examples in Groovy, it does not give examples in Python so I'm not sure where I'm going wrong.

Solution

Have a look at the 'Script Context Bindings' section here.

Basically a number of variables are available in the script context including: message,payload and log.

To return data using the python engine you set the result variable.

result = len(payload)

There is a example in the mule github.