[Zope-DB] Using <dtml-var>s in ZSQL methods?

[Ken Winter]

Here's the definition of a ZSQL method, "people_delete_by_id.zsql":

"
<dtml-comment>
  title: Method to delete People by ids given in a comma-separated list
  connection_id: my_database
  arguments:
	id_list
</dtml-comment>

delete from person 
where person_id in (<dtml-var id_list>)
"


Here's the puzzle:

When I define and test this ZSQL method through the ZMI, passing it a string
such as "9765, 10058, 11333", it indeed deletes the rows with those values
on person_id.

BUT when I invoke the same ZSQL method from a Python script with the
following code:

"
p = context.REQUEST.get('delete_this')
if p:
    s = ', '.join([str(x) for x in p])
    context.people_delete_by_id(id_list=s)
"

...and with a REQUEST variable 'delete_this' that comes from this snippet of
a form in a page template:

"
<form method="post" name="form2" 
	tal:attributes="action string:${here/absolute_url}/${template/id};">

<input type="hidden" name="form.submitted" value="1" />
<p class="error_message" tal:define="err errors/n|nothing"
	tal:condition="err"><b tal:content="err" /></p>
	
<table> 
	<tr tal:repeat="person options/data"><a name="id" id="id"
tal:attributes="name person/person_id"></a>
	    <td tal:condition="not:options/selectall | nothing"
		<input type="checkbox" name="delete_this:list:int" value="" 
			tal:attributes="value person/person_id"/>
	    </td>
...
	</tr>
</table>
...
</form>
"

...and with the same three person_ids (9765, 10058, 11333) the 4th line of
the Python script evokes an error:  

"
KeyError: 'id_list'
"

The core idea is that the string id_list is passed into the ZSQL method,
where it is spliced into the "delete...where" clause via the <dtml-var
id_list>) to provide the list of person_ids to delete.  


Here's the question:

WHY?

~ TIA
~ Ken

P.S.  I know that <dtml-var...> rather than <dtml-sqlvar...> is an
unorthodox and apparently undocumented construct to use within a ZSQL
definition.  But I need it because <dtml-sqlvar...> malformats the string.
And if doing this trick is a no-no, how come it works in the ZMI test but
not when called from Python?  More importantly, how can I get it to work
from Python?