Garbage collector strategy

[Martin Drautzburg]

Just for curiosity: does python use a mark-and-sweep garbage collector
or simple reference counting? In the latter case it would not garbage
collect circular references, right ?

For mark-and-sweep, I assume there must be a toplevel Object from
which all other objects can be accessed or they will be GCed (called
"Smalltalk" in Smalltalk). Is there such a thing?