Joseph Garvin <[EMAIL PROTECTED]> wrote: > When I first came to Python I did a lot of C style loops like this: > > for i in range(len(myarray)): > print myarray[i] > > Obviously the more pythonic way is: > > for i in my array: > print i > > The python way is much more succinct. But a lot of times I'll be looping > through something, and if a certain condition is met, need to access the > previous or the next element in the array before continuing iterating. I > don't see any elegant way to do this other than to switch back to the C > style loop and refer to myarray[i-1] and myarray[i+1], which seems > incredibly silly given that python lists under the hood are linked > lists, presumably having previous/next pointers although I haven't > looked at the interpeter source.
I think you'll find python lists are actually arrays not linked lists... > I could also enumerate: > > for i, j in enumerate(myarray): > print myarray[i], j # Prints each element twice > > And this way I can keep referring to j instead of myarray[i], but I'm > still forced to use myarray[i-1] and myarray[i+1] to refer to the > previous and next elements. Being able to do j.prev, j.next seems more > intuitive. Boundary conditions are a perenial problem in this sort of thing, what to do at the start / end of the list... > Is there some other builtin somewhere that provides better functionality > that I'm missing? I suppose you could use itertools... >>> from itertools import * >>> L=range(10) >>> (L1, L2, L3) = tee(L, 3) >>> L2.next() 0 >>> L3.next() 0 >>> L3.next() 1 >>> for prev, current, next in izip(L1, L2, L3): print prev, current, next ... 0 1 2 1 2 3 2 3 4 3 4 5 4 5 6 5 6 7 6 7 8 7 8 9 >>> -- Nick Craig-Wood <[EMAIL PROTECTED]> -- http://www.craig-wood.com/nick -- http://mail.python.org/mailman/listinfo/python-list
