How Do References In Functions Work?

First I wrote the first sample of code and it didn't work correctly. I prefer the first sample, but only the second one works correctly. I don't know why the first sample doesn't c

Solution 1:

You could also use [:], that will change the original object passed in:

def heap_sort(tab):
    heap = []
    for i in tab:
        heapq.heappush(heap, i)
    tab[:] = [heapq.heappop(heap) for _ in xrange(len(heap))]

So instead of reassigning the name tab to a new object you are actually updating the original tab object.

You could also use a generator expression instead of building the whole list:

tab[:] = (heapq.heappop(heap) for _ in xrange(len(heap)))

Solution 2:

Because you're just reassigning a new name called tab inside the function, it doesn't affect the global name tab you've defined. So, change your function to actually return the value, will work:

import heapq

defheap_sort(tab):
    heap = []
    for i in tab:
        heapq.heappush(heap, i)
    # return the supposed tab valuereturn [heapq.heappop(heap) for _ in xrange(len(heap))]

tab = [4, 3, 5, 1]
# assign the tab to the returned value
tab = heap_sort(tab)
print tab
[1, 3, 4, 5]

For your reference, read How do I pass a variable by reference? will help you understand how the referencing works in Python.

Solution 3:

Try this:

>>>defheap_sort(tab):
    heap=[]
    for i in tab:
        heapq.heappush(heap,i)
    heapq.heapify(heap)
    return heap

>>>t=heap_sort(t)>>>print(t)
[1, 3, 5, 4]