[mod_python] Detecting Back Button Usage

Clodoaldo clodoaldo.pinto.neto at gmail.com
Tue Mar 20 14:04:35 EST 2007

2007/3/20, Kenneth Loafman <kenneth at loafman.com>:
> Clodoaldo wrote:
> > 2007/3/20, Kenneth Loafman <kenneth at loafman.com>:
> >> I'm using mod_python under Ubuntu Edgy 64, doing some basic plots of
> >> data and allowing users to select a point to center on a region and gen
> >> the next plot.  All of that works as long as the user moves forward.
> >> The problem comes in the use of the back button.  The browser merely
> >> displays the last page rather than rebuilding it, or at least restoring
> >> the variables.  This leads to a lot of confusion because the server is
> >> on one set of plot values and the browser is now on another.  This seems
> >> to be a common problem.  Is there a solution, or should I just warn the
> >> user not to use the browser back button?
> >
> > How does the user select the point? Entering it in a form field? If so
> > save the plot values (the page state) on the page using a hidden field
> > inside the form:
> > <input type="hidden" name="variable_1" value="99.9">
> > <input type="hidden" name="variable_2" value="33.3">
> >
> > When the form is submitted those values will be available to your script.
> What I am doing is this:
> def regen_plot(req):
>     <plot logic snipped>
> return """\
> %s
> <div align="center">
> <a href="/demo/index/display_hit">
> <img src="/demo/%s.gif" ismap border=0></a>
> <p>X range is %d through %d seconds</p>
> </div>
> %s
> """ % (_head, dbname, xrng[0], xrng[1], _tail(req))
> Then when the user hits a point on the plot, display_hit is called.  I
> translate the x,y args from the URL into plot space, center the point
> around a smaller region, and plot again.  Going forward, it all works.
> Session() vars work, but since I'm not in a form, and there's no submit
> button, the hidden values don't work.  req.form.get('x') fails.
> Is it possible to get <form> to use an <img ... ismap> tag in lieu of
> the submit button?

I don't know. What if you just set the the values in the URL? This way
the user could even bookmark each frame of his interest.:

> <a href="/demo/index/display_hit?var_1=99.9&var_2=33.3">

Clodoaldo Pinto Neto

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