Introduction to Programming in Python, Aug-Dec 2011
                          Assignment 6
                  Due Monday, 24 October, 2011

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Instructions

** IMPORTANT: Note new policy regarding naming of zip file **

1. For each question, write a separate Python program with the
   filename indicated in the question.

   Zip your solutions into a single archive.  Use your CMI
   username to name the zip file (e.g. "madhavan.zip") and submit
   the zip file via moodle.

   If you don't name your zip file or the enclosed Python file
   correctly, you risk losing marks.

2. If the question asks for a function, you *must* write a
   function in Python (i.e., def f(x): ... )  Ensure that the
   function you define has the name indicated in the question.
   Also ensure that your function returns the value asked for,
   rather than printing it.

   If you add code to your file to test your function, make sure
   you *remove* this code when you submit your solution.  The
   Python file you submit should have *only* the function
   definition.

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NOTE: This assignment contains only one problem.  It is a
      reworking of Assignment 5 using Python classes.  

Filename: heapclass.py

Write a Python class that implements max-heaps.  The class should
be called Heap.  

An object h of type Heap should support the following operations:

   h.deletemax() :     deletes and returns the maximum element from
                       the heap and updates the heap accordingly

                       This function should raise an IndexError
                       exception with a suitable message if the
                       heap is empty.

   h.insertheap(val) : inserts val into the heap h

   h.heapsize()      : returns the number of elements in the heap

   str(h)            : returns a suitable string describing contents of h

When creating a heap, the default should be to create an empty
heap.  However, it should also be possible to supply an initial
list of values to be put into the heap.  For example:

   h1 = Heap()              # Creates an empty heap
   h2 = Heap([1,11,2,31])   # Creates a heap containing {1,11,2,31}

Note that the user supplies the initial values as a list, in
arbitrary order.  The class definition should ensure that these
values are organised as a max-heap.

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