Well, I've been way more "forget" than set". You are correct, the code I provided, originating from you years ago, is to extract !People\names from Keywords, in my case to use in a view I call Persons that nicely lists all the names, grouped, sorted, etc. That still works perfectly....IF the names are in Keywords in the !People\name format. What I've discovered is, they have stopped getting there. So, I asked the wrong question and provided the wrong code, sorry for the cloud of confusion.
The names were being put into field Keywords from field People. They were and still are put into People by Picasa. What is no longer happening is field People then populating field Keywords. What I have not located in my MC is any expression/code that would do this. Apparently I'm forgetting something, such as an external routine that reads People and populates Keywords.
It seems that whatever changed was almost 3 years ago, but I didn't notice. For photos that have People field values, I see Keywords populated with !People tags in Spring 2014, but by Fall 2014 I don't see Keywords !People tags in most photos that have People field values. (At times I have manually added !People tags to Keywords which confuses my history analysis.)
I usually update/upgrade MC promptly, so if I'm right about when MC versions switched, apparently the method was working in MC19 but stopped as of MC20. But somewhere in that same period I switched to a new PC running Windows 8, later upgraded to Windows 10. If anything external to MC was required, it might have gone missing at one of these transitions. I've learned the hard way that when MC does a version upgrade, it copies *almost* everything to the new version. What gets left behind is not identified or obvious, so I try to inspect the prior version and discover what I need to manually copy. But probably at the MC19-MC20 upgrade I missed something.
(A wonderful MC enhancement would be to have a specified folder to contain all user customizations -- visualizations, plug-ins, everything. MC would automatically scan this folder and treat whatever it finds as included in MC. MC would never touch this folder, and ideally MC could copy it during any upgrade. This is the safe-and-sane customization method used by a variety of development platforms, notably Drupal.)
But since my MC19 is long-gone, my trail has gone cold.
Background:
My workflow is this: I use Picasa to identify faces, which stores corresponding people names it its local system. Then, using the "experimental" option "Write faces to XMP", I cause Picasa to write the people names into the jpg files. MC then reads that data into its MJMD People field. In testing, that still works.
The need is to then have MC automatically read its own People field, and put each value into Keywords as !Person\value. This is what used to work, but now does not seem to. I'm still searching the forums, hoping to stumble across something.
PS: For those using Picasa for face recognition and tagging, there are various ways to do it.
Directly from Picasa, it seems (not really documented) that it will write face names to a tag that MC can read. The hidden trap is, "Write faces to XMP" must be manually triggered, easy to forget. There's no way to know which jpgs need it, so unless the action is run rigorously, the safe action is to select the entire library which can take a very long time to process. Even if being rigorous and careful, it might seem OK to choose only the newer photos to process, but any time a face-name gets added or changed, it can touch any number of photos here and there across the entire library. I recently updated the name of a cousin who got married, ran Write faces on just her Picasa People album, which then updated the People tag of her ancient grade school photos too, and also a bunch of family photos where she was just one among many, easily overlooked if Picasa had not identified her face in the crowd.
And/or, a powerful tool is AvPicFaceXmpTagger, which can read Picasa face names and put them into image files with several options.
http://www.anvo-it.de/wiki/avpicfacexmptagger:mainThe key is to send face names to one or more tags that MC can read.
Some of this is discussed here:
FaceTag Importer - Windows live gallery importer (but also Picasa)...
http://yabb.jriver.com/interact/index.php?topic=54119.0A 2009 discussion, older MC and older Windows. I'm exploring how applicable it is current versions.