name 'TO_VECTOR' is not defined : CSP Error

[mwaseem75]

Describe the bug
Getting the error while executing the below python code:
import iris
iris.sql.exec("DELETE FROM VectorLab")
stmt = iris.sql.prepare("INSERT INTO VectorLab (description,description_vector) VALUES (?, ?)")
for index, row in df.iterrows():
rs = stmt.execute(row['description'], TO_VECTOR(str(row['description_vector'])))

The error is:
CSPEvent+10^%CSP.Broker.1 *%Exception.PythonException 8 <class 'NameError'>:
iris version/image

python version
Is it a python3 or irispython. Not sure

To Reproduce
Steps to reproduce the behavior:
Just execute the above statement

Expected behavior
It should support to_vector() function.