On Sep 16, 2010, at 7:26 AM, Michael Ellis wrote: > > I was never much bothered by either of those issues, but there is one > bit of 'magic' that did (and to some extent still does) confuse me. > I'm wondering if it might be worthwhile to give an detailed > explanation what goes on in form.accepts(). > > When I first saw the idiom > > if form.accepts(): > ... > return dict(form=form) > > my assumption was that the call to form.accepts() was somehow > rendering and transmitting the page and waiting for a user response. > But then, I wondered how that could be since the form isn't passed to > the view until the return() is executed. Then I tried tracing a > controller and saw that it was being called multiple times. I got > lost down in the gluon code and more or less gave up trying to find > out exactly how the rabbit gets into the hat. Now I just use it and > trust that it works, but it still bothers me not to know what's going > on under the hood.
I've had the same reaction. The key to my understanding form.accepts, fwiw, was reading accepts itself. Keep in mind that web2py encourages form self-submission. That implies that the same code (controller/function) typically needs to run twice: once to create the page+form for display, and again to handle the form's submission. So form.accepts() is telling you whether it's the first time through, form creation (False) or the second, form submission (True). It's a little more complicated than that because of validation and error handling, but that's it in a nutshell.
