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

Peter Otten __peter__ at web.de
Wed Dec 4 10:50:52 CET 2013


Helmut Jarausch wrote:

> 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.

In that case have a look at bisect.insort() which adds an item to a list 
while keeping it sorted.




More information about the Python-list mailing list