Gerald Britton writes:
I was also wondering about garbage collection. If I have a humongous list, e.g. and "clear" it with:
mylist = []
does the old content not need to be garbage collected?
thislist = generate_me_a_humongous_list() thatlist = thislist thatlist = [] Definitely no garbage collection. The starting point of using garbage collection is that in general you don't know *locally* whether something is reachable or not. So you need to do a global analysis.
OTOH do dict.clear() and set.clear() immediately free their memory or does it just get queued for garbage collection?
This is covered in the manuals, but the gist is that every Python object knows how many other objects are pointing to it (called a refcount). When an object's refcount drops to zero, it gets collected (immediately, IIRC). However ... thislist = [] thatlist = [thislist] thislist.append(thatlist) and you have a reference cycle. These cycles are also collected, but this requires more effort, and so it is done only occasionally.