I am trying to build a heap with a custom sort predicate. Since the values going into it are of "user-defined" type, I cannot modify their built-in comparison predicate.
Is there a way to do something like:
h = heapq.heapify([...], key=my_lt_pred)
h = heapq.heappush(h, key=my_lt_pred)
Or even better, I could wrap the heapq functions in my own container so I don't need to keep passing the predicate.
The heapq documentation suggests that heap elements could be tuples in which the first element is the priority and defines the sort order.
More pertinent to your question, however, is that the documentation includes a discussion with sample code of how one could implement their own heapq wrapper functions to deal with the problems of sort stability and elements with equal priority (among other issues).
In a nutshell, their solution is to have each element in the heapq be a triple with the priority, an entry count and the element to be inserted. The entry count ensures that elements with the same priority a sorted in the order they were added to the heapq.