On Tue, 03 Dec 2013 13:06:05 +0000, Duncan Booth wrote: > Helmut Jarausch <[email protected]> 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) >> >> # 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 all you want to do is pull all of the elements out of the heap in > order, you would probably be better off just doing: > > for N in sorted(H): > print(N) > > Heaps are mostly useful if you want only some of the elements, or if you > are continually producing more elements while also processing the > smallest ones. > > However, if you really wnt to do this: > > for N in iter(lambda: heappop(H) if H else None, None): > print(N) > > will work so long as H cannot contain None. If it can just replace both > occurences of None with some other sentinel: > > sentinel = object() > for N in iter(lambda: heappop(H) if H else sentinel, sentinel): > print(N) > > > Alternatively your 'in_sequence' function would look better without the > exception handling: > > def in_sequence(H) : > while H: > yield heappop(H)
Many thanks! And as noted in another reply, I try to overlap CPU time with file I/O since I have to open / read / close a file for each line that gets pushed onto the heap. Helmut -- https://mail.python.org/mailman/listinfo/python-list
