Santiago Caracol wrote: > Hello, > > I want to write a web application that does this: > > (1) The user submits a query: > > --------------------------------- > | What is the answer? | > --------------------------------- > <Submit> > > (2) The web server gives the user N answers and a button saying "More > answers": > > . answer 1 > . answer 2 > . answer 3 > > <More answers> > > I am aware of several ways to do this: I could calculate all > answers, but show only the first N of them. For certain kinds of > calulations, > I could use a kind of setoff argument. But I would like to do it in a > more general > and (hopefully) efficient way: > > I want the function or object that calculates the answers to be > "frozen" at the point at which it has already calculated N answers. If > the function gets a <More answers>-signal within a reasonable period > of time, it goes on producing more answers exactly at the point at > which it got frozen. If no signal is sent, the function call is > terminated automatically after > M seconds. > > Note that, although the program to be written is a web application, > this is not a question about web application specific things. My only > difficulty is how to "freeze" function calls. > > Has anyone done something of this kind?
Python offers an elegant mechanism to calculate values on demand: the generator function: >>> def calculate_answers(): ... for i in range(100): ... print "calculating answer #%d" % i ... yield i * i ... >>> from itertools import islice >>> gen = calculate_answers() This builds the generator but doesn't run the code inside. Now let's look at the first three "answers": >>> for answer in islice(gen, 3): ... print "the answer is", answer ... calculating answer #0 the answer is 0 calculating answer #1 the answer is 1 calculating answer #2 the answer is 4 If you repeat the last step you get the next three answers: >>> for answer in islice(gen, 3): ... print "the answer is", answer ... calculating answer #3 the answer is 9 calculating answer #4 the answer is 16 calculating answer #5 the answer is 25 Peter -- http://mail.python.org/mailman/listinfo/python-list
