I'm using the PEX framework to create non-polling Business Services in Python. Below is the code I've used to instantiate my Python Business Service from the application I have written:

conn = iris.connect(...)
IRIS = iris.createIRIS(conn)
#...#
pexserv = iris.pex.Director.CreateBusinessService(conn, "Demo.PEX.FlaskPEXService")
response = pexserv.ProcessInput(record_id)
IRIS.close() # Release IRIS obj
conn.close()

I'm curious about how embedded Python is handled by %CSP classes, particularly in the case of defining REST endpoints on IRIS.
Here is a simple dispatch class for the endpoint /api/pythonapp on my local IRIS instance (2022.3):

Class Python.App.Dispatch Extends %CSP.REST
{

XData UrlMap [ XMLNamespace = "https://www.intersystems.com/urlmap" ]
{
<Routes>
    <Route Url="/test" Method="GET" Call="Hello" />
</Routes>
}

ClassMethod Hello() As %Status [ Language = python ]
{
    import iris

    print('Hello World!