Thanks @Ben Spead! It was fun to do and hope it helps (in a small way) increase people's use/understanding of embedded python. 

Please check out this documentation, where there is an example of using an array holding the sql statement:

%SQL.Statement - InterSystems IRIS Data Platform 2021.2 - including private class members
 

According to that document, the query your code builds and passes to %Prepare is "UPDATE QUERY UPDATE QUERY", which is not valid.

You're welcome Andy