heapify returns NoneType

Question

I have the following code:

b = heapify([5,4,9,1])

and when I check for the following

type(b)

It shows it's NoneType instead of list type. How do I fix this issue?

Answer 1

The heapify() method transforms the list in-place. This means that it alters the list, but does not return the modified list. As agf mentions below, heapify() returns None to protect you from this mistake. Therefore, if you do

lst = [5,4,9,1]
heapify(lst)
type(lst)

you will see that lst is now heapified.