[Python-Dev] Re: heaps (original) (raw)

Michael Chermside mcherm@mcherm.com
Tue, 6 May 2003 05:32:03 -0700

Zooko writes:

Shouldn't heapq be a subclass of list? [...] One thing I don't know how to implement is:

# This changes mylist itself into a heapq -- it doesn't make a copy of mylist! makeheapq(mylist) Perhaps this is a limitation of the current object model? Or is there a way to change an object's type at runtime.

To change an object's CLASS, sure, but it's TYPE -- seems impossible to me on the face of it since a different type may have a different C layout. Now in THIS case there's no need for a different C layout, so perhaps there's some wierd trick I don't know, but I wouldn't think so.

As to your FIRST point though... the choice seems to be between making heapq a subclass of list or a module for operating on a list. You argue that the syntax will be cleaner, but comparing your examples:

heap = [] heappush(heap, item) item = heappop(heap) item = heap[0]

heap = heapq() heap.push(item) item = heap.pop() item = heap[0]

I honestly see little meaningful difference. Since (as per earlier discussion) heapq is NOT intended to be a abstract heap data type, I tend to prefer the simpler solution (using a list instead of subclassing).

-- Michael Chermside