extracting a heapq in a for loop - there must be more elegant solution

Peter Otten __peter__ at web.de
Tue Dec 3 13:38:58 CET 2013


Helmut Jarausch wrote:

> Hi,
> 
> I'd like to extracted elements from a heapq in a for loop.
> I feel my solution below is much too complicated.
> How to do it more elegantly?
> I know I could use a while loop but I don't like it.
> 
> Many thanks for some lessons in Python.
> 
> Here is my clumsy solution
> 
> from heapq import heappush, heappop
> # heappop raises IndexError if heap is empty
> 
> H=[]
> for N in 'H','C','W','I' :
>   heappush(H,N)

H = ["H", "C", "W", "I"]
heapq.heapify(H)

But see below.

> # how to avoid / simplify the following function
> 
> def in_sequence(H) :
>   try :
>     while True :
>       N= heappop(H)
>       yield N
>   except IndexError :
>     raise StopIteration
> 
> # and here the application:
> 
> for N in in_sequence(H) :
>   print(N)

If you are iterating over the complete heap I see no advantage over a sorted 
list. So

for N in sorted(H):
    print(N)

If H is huge use H.sort() instead of sorted() to save memory.
If you need only a few items use heapq.nsmallest().




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