Itertools `tee` does not seem to de-reference yielded items, even after consumption of all items from all tee-iterators.

According to the documentation (to my understanding), there shouldn't be any extra memory requirement as long as the tee-iterators are consumed in a balanced way. I.e. after an item was pulled from all iterators there shouldn't be any residual reference to it.

This is true for the example-implementation mentioned in the documentation, but `itertools.tee` doesn't de-reference items until the tee-iterator itself is deleted:

https://pastebin.com/r3JUkH41

Is this a bug or am I missing something?

Whats going on is that the implementation tracks blocks of 56 references at a time, freeing entire blocks at time.   So the memory release does occur periodically, but not as aggressively as it could. This code shows what is going on:

    # Show the timing of when objects are decreffed

    from itertools import tee

    class Notify:
        def __init__(self, x):
                self.x = x
        def __del__(self):
                print('<Clearing: %r>' % self.x)
        def __repr__(self):
                return 'Notify(%r)' % self.x

    it = map(Notify, range(100))
    p, q = tee(it)
    for i in range(100):
        next(p)
        next(q)
        print(i)
    print('Deleting it')
    del it
    print('Deleting p')
    del p
    print('Deleting q')
    del q

I'll look to see if the objects can be freed sooner without doing major brain surgery to the existing code.

I've just reviewed the code.  The observed behavior is an intrinsic part of the design and was an expected behavior (noted in the comments).  I don't see a non-invasive way of making the memory releases more aggressive.