On 22 November 2017 at 11:00, Chris Angelico <rosuav@gmail.com> wrote:
So the question is more: why, with Python being the way it is, do the
heap functions operate on a list? I think heapq.heapify is the answer:
in linear time, it heapifies a list *in place*.

I don't think there's any reason to have *both* interfaces to the heap
functionality, but it certainly isn't illogical to try to treat a heap
as a thing, and therefore have a Heap type.

Right, the parallel here is that we have a "heapq" module for the same reason that we have list.sort(), sorted(), and the bisect module, rather than a single "SortedList" type. https://code.activestate.com/recipes/577197-sortedcollection/ then provides an example of how to combine those into a "SortedCollection" type.

That said, I'm still in favour of adding an object-oriented wrapper to either `collections` or the `heapq` module for all the classic OO reasons:

- it makes it easier to reliably maintain the heap invariant (just drop your list reference after passing it to the heap wrapper)
- it gives both human readers and static code analysers more information to work with ("this is a heap" rather than "this is a list")
- it provides a hook for improved interactive help on heap instances

I don't have any great concerns about potential confusion - the OO wrapper will be easy enough to use that anyone that's unsure will likely gravitate towards that, while the lower level `heapq` functions will remain available for folks writing their own heap implementations.

This effect would likely be even more pronounced if the OO wrapper were made available as `collections.Heap` (`collections` already imports the `heapq` module for use in the Counter implementation).


Nick Coghlan   |   ncoghlan@gmail.com   |   Brisbane, Australia