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Posted to users@httpd.apache.org by Simon Hook <si...@jpl.nasa.gov> on 2005/03/10 07:23:12 UTC
[users@httpd] When an image is replaced in the htdocs directory through a cgi script and incorporated into a new html page the new image does not get incorporated.

PROBLEM: When an image is replaced in the htdocs directory through a cgi 
script and incorporated into a new html page the new image does not get 
incorporated.

Hi All,

I am trying to write a web app where a variable, passed with a form, is 
used to generate a plot, which is saved and then displayed  as a static 
image in an html page. I am using the webform from pythonweb and 
generating the plot with matplotlib. I am using Apache 2.053 under 
Windows XP. I am keeping it real simple by simply passing an integer. 
The whole process works, HOWEVER, when I back page and submit a new 
integer value which  generates a new plot and new static image, the new 
image does not get displayed, instead the last version of the static 
image (plot) is displayed (presumably from the cache). If I reload the 
page with the browser the updated image gets displayed otherwise the 
previous plot gets displayed with 2  or 3 re-submits and then eventually 
an updated one is displayed. It seems like Apache does not recognize a 
changed image and still uses the first plot I created for 2 or 3 submits 
or the submit does not force Apache to look for a changed file.

I am new to Apache, Pythonweb and MatplotLib although I have done 
similar stuff with ASP and IIS and some Python work. I have waded 
through the Apache and Pythonweb  documentation and got nowhere. I have 
tried using the MOD_EXPIRES directive with Apache but this has no 
effect. I think this is because a new image (PNG)  has been generated 
rather than an old one has expired. I cannot see any way with pythonweb 
forms to load a static html page (i.e. with cgi). I think if I had a 
static html page I could write out maybe I could expire that which would 
force Apache to load the new image file.

I have tried

<META HTTP-EQUIV=Refresh CONTENT=1>

which refreshes the page every second - this works but who would want it!

I have tried

<META HTTP-EQUIV=expires CONTENT=0>

but this does not work.

I have attached the code below, its a rework of one of the examples in 
pythonweb. Just copy this to the cgi-bin directory and it should work, 
provided matplotlib is installed. Matplotlib is available from:

http://matplotlib.sourceforge.net/

Pythonweb is available from:

http://www.pythonweb.org

Despite hours of trying I cannot get this to work, which would seem like 
a necessity for Pythonweb and Apache. Any help would be much appreciated.

Thanks,

Simon

---cut here

#!d:/apps/Python23/python

"The form that will not update"

import sys, re, os
sys.path.append('../')
sys.path.append('../../')

import web.error; web.error.handle(handler='browser', output='debug', 
format='html')
import web, web.form, web.form.field.basic, web.util
import web.form.field.typed
from pylab import *

class ExampleForm(web.form.Form):
   
    def setup(self):
        self.addField(web.form.field.typed.Integer('myval', default=6, 
required=True))
       
        # The preffered way of adding submit buttons is as actions so 
Submit buttons are normally not used.
        self.addAction('Validate This Form')

# Print the HTTP Header
print web.header('text/html')

# Create a form
exampleForm = ExampleForm('form', os.environ['SCRIPT_NAME'], 'get')

if len(web.cgi) > 0: # Form submitted
    # Populate form with the values from get.
   
    # Populate the form
    exampleForm.populate(web.cgi)   
               
    # Process the form (Validate)
    if exampleForm.valid():               
               
        # Grab the desired value, from the form
        myval=exampleForm['myval'].value
               
        # Create the plot, saved as a png in the htdocs directory
        myarray=[myval,4,9,16]
        print myarray
        plot([1,2,3,4], myarray, 'ro')
        axis([0, 6, 0, 20])
        savefig('../htdocs/plot.png')
       
        print "<hmtl><body><div align=center><img src=/plot.png 
alt=theplot></div></body></html>"

else:
    print "<html><head><title>noupdate</title></head><body>\n<h1>Input 
integer 0-10</h1>%s\n<hr></body></html>"%(exampleForm.html())

---end cut

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