# FAQ: Heaps: Python - Min-Heap Review

This community-built FAQ covers the “Min-Heap Review” exercise from the lesson “Heaps: Python”.

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Here’s an application for min_heap: a sorting algorithm.

1 Like

Is it okay if I change this part

min = self.heap_list[1]
self.heap_list[1] = self.heap_list[self.count]
self.count -= 1
self.heap_list.pop()
self.heapify_down()
return min

to

min = self.heap_list[1]
self.heap_list[1] = self.heap_list.pop()
self.count -= 1
self.heapify_down()
return min

@beowolve, it looks good, since the expressions `self.heap_list[self.count]` and `self.heap_list.pop()` appear to do the same thing.

However, it fails when you are down to one element. At that point, the heap looks something like, [None, 10], and the assignment statement

`self.heap_list[1] = self.heap_list.pop()`

… will return an Index Error, since when an assignment statement is executed, the first thing that happens is that the expression on the right, `self.heap_list.pop()`, is evaluated. That removes the final item from the list, whose length is reduced from two to one…

When the second part of the assignment takes place, assigning the value returned from the right side to the variable on the left, the interpreter looks for self.heap_list[1] to which to assign the popped value, but it is not there; hence the IndexError.

2 Likes

I see~
Thank You!!

1 Like