I just verified that neither class nor routing mapping works with embedded Python.
Not even the elementary trick to have it as a %Z* class in %SYS.
This applies also to 2022.1 preview. The BUG is logged at WRC.
I share your disappointment.

Hello Peter,
Like you, I have an > 40-year history with MUMPS dating back before DSM-11.
Not every implementation of the global storage was effíent (no names, no finger-pointing)
What you see today in IRIS is the result of continuous effort on improving performance
and storage efficiency.
In past, the size of a physical disk was the limit. Today with virtual storage systems the
limit is set only by the file system used. This is a fact that InterSystems lives with since "ever". 
A word concerning global efficiency:
Multiple experiences over years showed me that the space consumption with IRIS and 
its predecessor Caché was always significantly lower than with the various source  DBs
I was invited to migrate.  With Sybase, it was rather more impressive than with others.
The immediate consequence of this high efficient storage technology is the gain in speed.
Also with the most modern technologies, there is still a transfer between persistent 
storage  (aka. disk) and memory.  And the less you have to transfer the faster you are.
 
Finally, welcome to this society!
Robert
 

But be aware to have the method SetNamespace available also the new target namespace to be able to return !
So you either map the class to Namespace %All,
or name the class %ZEmbedded.Utils or similar,  to make it available across all namespaces.

I couldn't identify in my examples any $LB(),$LI(), $LV,$LL()  like feature.
- In the mixed PY/ISOS example I just called from PY a method in ISOS [ = InterSystems ObjectScrtipt]
- in the PY pure I kept the binary string as found and reloaded it the same way.
  

AS you push on "nothing in memory" which is not related at all to INDIRECTION 
I have streamlined your code to not leave any traces in memory.

 
ClassMethod PPG() {
 set TABLES(0)="EVEN",TABLES(1)="ODD"
 kill ^||Arturo
 for i=1:1:100 set ^||Arturo(TABLES((i#2)),i)=i 
 set evenTotal=0
 set i=""  if $D(^||Arturo("EVEN",0))
 for  set i=$ORDER(^(i),1,val) QUIT:i=""  if $i(evenTotal,val) 
 zwrite evenTotal kill ^||Arturo QUIT}

OLÉ

to allow Indirection in your case or eXecute to work, you have to set  

ClassMethod Indirection() [ ProcedureBlock=0 ] 

see:  https://docs.intersystems.com/iris20212/csp/docbook/DocBook.UI.Page.cls?KEY=ROBJ_method_procedureblockand my related article: https://community.intersystems.com/post/summary-local-variable-scoping

upgrade version ?

It should be sufficient to add this to init:script

set user=##class(Security.Users).%OpenId("unknownuser")
do user.Roles.Insert("%All")
do user.%Save()
 ;;; just for comfort
set smp=##class(Security.Applications).%OpenId("/csp/sys")
set smp.AutheEnabled=64
do smp.%Save()

set