I have a soft corner for TCL, because of its idiosyncracies and weird dynamic stringy playfulness. I would be wary of using it professionally but to play around for the fun of it ... it's just too much fun. Upvar and uplevels are crazy.

Python is that kind of cool one behaves when visiting parents of your would be spouse for the first time. Tcl on the other hand is like playing one's secret exclusive and somewhat dangerous games with kid school bestie.

Tcl/Tk pioneered the notion of a scripting language as a library. It got threading right. You can run multiple independent Tcl interpreters in the address space of your process and they can exchange messages. Entirety of interpreter state is encapsulated inside the interpreter object, no globals. To a user an it is just a pointer to an object.

No need for GIL, no need for serialization/deserialization (pickle/unpickle) ... just within process memory copy (or no copies in case data is immutable).