[docs] Heapq documentation bug

[Johannes Hoff]

Hi,

There is, in my opinion, a bug in the documentation for heapq, for all
versions of this module [1].

The documentation states the following:

> Heaps are arrays for which heap[k] <= heap[2*k+1] and heap[k] <= heap[2*k+2] for all k

In this context, I would say that "heaps" clearly refers to the
general concept, not this particular implementation. In that case, it
is not correct to say that heaps are arrays - they are trees. They are
often implemented as arrays, but they need not be.

Sources:
http://en.wikipedia.org/wiki/Heap_(data_structure)
http://c2.com/cgi/wiki?HeapDataStructure

Suggested wording:

> Heaps are trees for which every parent node has a value less than or equal to any of its children. This implementation uses an array for which heap[k] <= heap[2*k+1] and heap[k] <= heap[2*k+2] for all k, counting elements from zero. For the sake of comparison, non-existing elements are considered to be infinite. The interesting property of heaps is that the smallest element is always the root, in this case heap[0].

Or, dropping the general case:

> This implementation stores the heap in an array for which heap[k] <= heap[2*k+1] and heap[k] <= heap[2*k+2] for all k, counting elements from zero. For the sake of comparison, non-existing elements are considered to be infinite. The smallest element of the heap will always be at the root, heap[0].

Johannes

[1] See latest python 2: http://docs.python.org/library/heapq
and python 3: http://docs.python.org/py3k/library/heapq.html