Peeking in a heap in python

Yes, you can make this assumption, because it is stated in the documentation:

Heaps are arrays 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 a heap is that
heap[0] is always its smallest
element.

(And that’s probably the reason there is no peek function: there is no need for it.)