Hi,

I am working on a project (nevow + twisted) where lots of statistical computing is done using “R”, interfaced by rpy.py. It works very well. To be able to parameterize the computing, I defined an additional namespace and put the parameters with this namespace inside the nevow templates. It looks like:

<html xmlns:nevow="http://nevow.com/ns/nevow/0.1"

xmlns:new_namespace="http://new_namespace.de/ns/0.1"

xmlns="http://www.w3.org/1999/xhtml"

xml:lang="de" lang="de">

<head>

</head>

<body>

<img

new_namespace:title="Fehlerklasse 2 (letzte 50)"

new_namespace:table="defect"

new_namespace:fields="measurement_id gravity"

new_namespace:reorder_x="1"

new_namespace:reverse_x="1"

new_namespace:sql="class = 2 ORDER BY _id DESC LIMIT 50"

new_namespace:function="errorplot"

new_namespace:smooth="2"

nevow:data="Measurement"

nevow:render="Plot">

</body>

</html>

The parameters are extracted like this:

def data_Measurement (self, context, data):

"""Extracts the parameters from the attribute-list.”.

self.html_params = {}

self.script_params = None

todelete = []

for theKey in context.tag.attributes:

keyFound = False

if type(theKey) is tuple:

if len(theKey) == 2:

ns = theKey[0]

tag = theKey[1]

if ns == u'http:// new_namespace.de/ns/0.1' :

name = tag

value = context.tag.attributes.get(theKey)

self.script_params[name] = value

## Append the key to the list of keys to remove later.

## Unfortunately the parameters must be cleared, so that only valid attributes

## according the html-element are present in the rendering step.

todelete.append(theKey)

## Delete the param-keys from the attribule-list.

## Otherwise the attributes would be present in the rendering and this is for the birds.

for theKey in todelete:

del context.tag.attributes[theKey]

In the function render_measurement() the function is called with the parameters (in this case “errorplot”) and the resulting image is rendered. This also works very well. My question is: Is there a better and simpler way to do that? And if not, why do I have to remove the additional attributes, because later on nevow gets confused about this attributes and produces a nice stack-trace?

The next question is: In the render_whatever() functions an image is produced, and I want to write the image directly with perhaps request.write(). How can this be done using nevow?

Thanks,

Werner