How to pass a dtml-var to a python script.

[Mike]

I am New to python and Zope and am confused about how to pass a value
I hold inside of a <dtml-var ... > to a python script: here's what I
am doing(or doing wrong):

<dtml-var "ContextSession(REQUEST)">
<dtml-let choices="REQUEST.SESSION['choices']">
<dtml-let myTissue="choices['tissue']">
<dtml-let myHistology="choices['histology']">
<dtml-let mySubtype="choices['subtype']">
<dtml-var "CMAPContext(CORE_HOST, 'Context.jsp', myTissue,
myHistology, mySubtype)">

ContextSession is a python script that extracts parameters from the
URL and puts
them inside of the REQUEST.SESSION.choices placeholder. I then want to
take them
out of the session and pass them to the CMAPContext() python script,
but the way I am doing it doesn't work and I can't find any
documentation on how to do this.

Thanks,

Mike