Python script to generate a heap by the downward method.

heap_downward.py

#! /usr/local/bin/python3.6
"""
Heap generation with the downward method
"""
import random
import sys


class Heap:
    N = 100  # Number of data

    def __init__(self):
        self.heap = [0]
        for _ in range(self.N):
            self.heap.append(random.randrange(self.N) + 1)
        self.__display(0)

    def generate(self):
        """ Heap generation """
        try:
            n = self.N
            for i in range(int(n / 2), 0, -1):
                p = i
                s = 2 * p
                while s <= n:
                    if s < n and self.heap[s + 1] < self.heap[s]:
                        s += 1
                    if self.heap[p] <= self.heap[s]:
                        break
                    self.__swap(p, s)
                    p = s
                    s = 2 * p
            self.__display(1)
        except Exception as e:
            raise

    def __swap(self, a, b):
        """ Swapping

        :param int a: index of heap list
        :param int b: index of heap list
        """
        try:
            w = self.heap[a]
            self.heap[a] = self.heap[b]
            self.heap[b] = w
        except Exception as e:
            raise

    def __display(self, k):
        """ Display

        :param int k: 0: list of tree,
                      1: list of heap
        """
        try:
            print("#### ", end="")
            if k == 0:
                print("Tree")
            else:
                print("Heap")
            for i in range(1, self.N + 1):
                print("{:5d} ".format(self.heap[i]), end="")
                if i % 10 == 0 or i == self.N:
                    print()
        except Exception as e:
            raise


if __name__ == '__main__':
    try:
        obj = Heap()
        obj.generate()
    except Exception as e:
        print("EXCEPTION!", e.args, file=sys.stderr)
        sys.exit(1)