[issue32142] heapq.heappop - documentation misleading or doesn't work

[Scott Queen]

New submission from Scott Queen <scooter4j at gmail.com>:

The documentation for heapq.heappop(heap) says:
"Pop and return the smallest item from the heap, maintaining the heap invariant. If the heap is empty, IndexError is raised. To access the smallest item without popping it, use heap[0]."

yet, in the following code, the resultant heap doesn't reflect the heap invariant:

import heapq
li = [5, 7, 9, 1, 4, 3]
heapq.heapify(li)
#change a couple values in the heap
li[3] = 16
li[4] = 2
print (heapq.heappop(li))
print ("The heap after pop is : ",end="")
print (list(li))

This prints: The heap after pop is : [3, 4, 9, 16, 2]

The documentation implies to me that heapify would be called internally after heappop, but I may be misreading. Perhaps heappop could say that the heap invariant is maintained if the heap is properly sorted before the heappop invocation.

----------
assignee: docs at python
components: Documentation
messages: 307006
nosy: docs at python, scooter4j
priority: normal
severity: normal
status: open
title: heapq.heappop - documentation misleading or doesn't work
type: behavior
versions: Python 3.6

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32142>
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