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

[Helmut Jarausch]

On Tue, 03 Dec 2013 13:38:58 +0100, Peter Otten wrote:

> 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().


Many thanks!
In my real application the data which is pushed onto the heap will be extracted from a small file
which is executed several thousands times. So, I thought, I could keep the CPU a bit busy while
the OS is doing file I/O. Of course, I could have appended all these strings to a list which is
sorted at the end.