> On Fri, May 31, 2013 at 2:58 AM, rusi wrote: > > On May 30, 5:58 pm, Chris Angelico wrote: > > > The alternative would be an infinite number of iterations, which is far > > > far worse. > > > > There was one heavyweight among programming teachers -- E.W. Dijkstra > > -- who had some rather extreme views on this. > > > > He taught that when writing a loop of the form > > > > i = 0 > > while i < n: > > some code > > i += 1 > > > > one should write the loop test as i != n rather than i < > > n, precisely because if i got erroneously initialized to > > some value greater than n, (and thereby broke the loop > > invariant), it would loop infinitely rather than stop > > with a wrong result. > > > > And do you agree or disagree with him? :) I disagree with > Dijkstra on a number of points, and this might be one of > them. When you consider that the obvious Pythonic version > of that code: > > for i in range(n,m): > some code
Maybe from your limited view point. What if you need to perform operations on a sequence (more than once) in a non-linear fashion? What if you need to modify the sequence whilst looping? In many cases your simplistic "for loop" will fail miserably. py> lst = range(5) py> for n in lst: ... print lst.pop() 4 3 2 Oops, can't do that with a for loop! py> lst = range(5) py> while len(lst): ... print lst.pop() 4 3 2 1 0 -- http://mail.python.org/mailman/listinfo/python-list
