Thanks, Jonathan. That's approximately what I had reasoned it must be doing, but couldn't state as clearly as you have.
So, if I'm now understanding it correctly, form.accepts() is roughly equivalent to the following conditions: (request contains submitted form elements) and (form key matches) and (all elements pass validation) The 'magic' is simply that clicking the submit button sends a second request to the controller that created it. So the form object only *seems* to persist; in actuality, it's recreated from scratch when the second request comes in. All of which explains why I was unable to store extra info in the form object at view time and have it available after form.accepts() came back True. Is that a fair summary of how it works? On Thu, Sep 16, 2010 at 11:04 AM, Jonathan Lundell <jlund...@pobox.com>wrote: > 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. > > >
