If you have a dataset that takes UUIDs as input, a dataset will often pass these directly to postgres, causing a failure such as 

psycopg2.errors.InvalidTextRepresentation: invalid input syntax for type uuid: "a" LINE 12: IN ('a', 'b', 'c')

These parameters should be validated before use. The easiest way might be for Q{{uery}}s to specify an 'input validator' that is called on each input before passing data into fetch