On Mon, 13 Mar 2006 17:24:31 -0800, Raymond Hettinger wrote: > John Savage wrote: >> Could >> someone please explain the rationale behind python designers' thinking >> in deciding the function "range(1,12)" should return the sequence 1 to >> 11 rather than the more intuitively-useful 1 to 12?? > > There are several ways to do this, closed intervals, half-open > intervals, zero indexed, indexed from one, etc. Each way has its own > strengths and weaknesses. Guido chose the one he liked best and > applied the concept consistently throughout the language (slicing, > etc). His choice has some nice properties such as len(range(n))==n and > range(0,i)+range(i,n)==range(n). > > The downside of the half-open interval approach is that it can be > confusing when counting backwards: range(n-1, -1, -1). Accordingly, > the builtin reversed() function was introduced so you could write this > in a more intuitive and readable manner: list(reversed(range(n))). > > Some of this is a matter of taste and a matter of what you're used to > using, so the answer to what is the "more intuitively-useful" varies > depending on who is answering the question.
It is true that *some* of this is just a matter of taste, but more importantly, *much* of this is a matter of objective superiority. See, for example: http://lists.canonical.org/pipermail/kragen-tol/2004-March/000757.html http://www.jaggersoft.com/pubs/HowToWriteALoop.htm#Half-Open%20Interval This thread discusses why a closed interval is better: http://mail.python.org/pipermail/edu-sig/2004-April/003747.html As near as I can tell from reading it, the sole reason a closed interval is better is that in common English phrases "x to y" usually (but not always) means the closed interval including both x and y. A very common error in programming is the so-called fencepost error. Half-open intervals help avoid them, while closed intervals tend to result in this bug. http://en.wikipedia.org/wiki/Fencepost_error In other words, while the choice of half-open intervals is partly a matter of taste, Guido is no dummy. Most of the time, his taste is influenced by practical matters, and this is one of those times. Half-open intervals will naturally help you avoid bugs. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
