In one application, I would like to use a heap as an allocation pool. I also want to check that a given value isn't released twice, therefore that the heap contains unique values. My use case would be solved nicely if heappush() took an optional "unique=False" parameter.

Note that I haven't checked if doing so is possible while maintaining the O(log n) complexity :-)

No, it's impossible without additional structure. And with a set it is trivial.

def uniqueheappush(heap, inheap, item):
    if id(item) in inheap:
        return False
    heappush(heap, item)
    inheap.add(id(item))
    return True

def uniqueheappop(heap, inheap):
    item = heappop(heap, inheap)
    inheap.discard(id(item))
    return item

I recomend reject this issue.

> No, it's impossible without additional structure. And with a set it is trivial.

Yeah, I wanted to avoid the memory overhead of a set.

I would dedup when extracting items from the queue, because it is trivial to find duplicates then. It can be done with a simple wrapper, without any changes to the queue.