Python: does the class class set a "leak" when elements are deleted, for example, dict?

Question

I know that a Python dict will “leak” when the elements are deleted (because the element slot will be overwritten with the magic “deleted” value) ... But will the set class behave the same? Is it safe to keep set around, add and remove things from it over time?

Edit : Ok, I tried, and here is what I found:

  >>> import gc
 >>> gc.collect ()
 0
 >>> nums = range (1000000)
 >>> gc.collect ()
 0
 ### rsize: 20 megs
 ### A baseline measurement
 >>> s = set (nums)
 >>> gc.collect ()
 0
 ### rsize: 36 megs
 >>> for n in nums: s.remove (n)
 >>> gc.collect ()
 0
 ### rsize: 36 megs
 ### Memory usage doesn't drop after removing every item from the set ...
 >>> s = None
 >>> gc.collect ()
 0
 ### rsize: 20 megs
 ### ... but nulling the reference to the set * does * free the memory.
 >>> s = set (nums)
 >>> for n in nums: s.remove (n)
 >>> for n in nums: s.add (n)
 >>> gc.collect ()
 0
 ### rsize: 36 megs
 ### Removing then re-adding keys uses a constant amount of memory ...
 >>> for n in nums: s.remove (n)
 >>> for n in nums: s.add (n + 1,000,000)
 >>> gc.collect ()
 0
 ### rsize: 47 megs
 ### ... but adding new keys uses more memory.

Answer 1

Yes, set is basically a hash table, like dict - differences in the interface do not imply many differences below. From time to time you should copy the set - myset = set(myset) - just like you should for the dict, according to which many additions and deletions are regularly performed over time.

Answer 2

For such questions, it is often better to conduct a quick experiment like this and see what happens:

 s = set() for a in range(1000): for b in range(10000000): s.add(b) for b in range(10000000): s.remove(b) 

What documents and people say and what kind of behavior is actually happening often diverge. If this is important to you, check it out. Do not rely on others.