[mod_python] Detecting Back Button Usage

Kenneth Loafman kenneth at loafman.com
Tue Mar 20 13:46:35 EST 2007

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 """\
<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>
""" % (_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?


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