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copied!<p>The natural way to persist the data among different submits is by using the <a href="http://code.google.com/appengine/docs/python/gettingstarted/usingdatastore.html" rel="noreferrer">Datastore</a>.<br> If, for exercise, you don't want to use the datastore, you are forced to pass the data to the view and read it back using some <code>hidden</code> fields between each web request.</p> <p>Let's see an easy <em>quick&dirty</em> example: a web app that sums integers one by one.</p> <p><strong>application.py</strong></p> <pre><code>import os from google.appengine.ext import webapp from google.appengine.ext.webapp import template from google.appengine.ext.webapp.util import run_wsgi_app class Sum(webapp.RequestHandler): def get(self): path = os.path.join(os.path.dirname(__file__), 'index.html') template_values = {"total":0} self.response.out.write(template.render(path, template_values)) def post(self): value = self.request.get("value") total = self.request.get("total") total = int(total) + int(value) path = os.path.join(os.path.dirname(__file__), 'index.html') template_values = {"value":value, "total":total } self.response.out.write(template.render(path, template_values)) application = webapp.WSGIApplication( [('/', Sum), ('/sum', Sum)], debug=True) def main(): run_wsgi_app(application) if __name__ == "__main__": main() </code></pre> <p>To pass the data to the <code>index.html</code> view, the template.render function is used passing a dictionary variable that carries the result to the view:</p> <pre><code>template.render(path_to_the_view, template_values) </code></pre> <p><strong>index.html</strong></p> <pre><code><html> <body> <form action="/sum" method="post"> <p> <label for="value">Value to sum: <input type="text" name="value"><br> <input type="submit" value="Submit"> <input type="hidden" name="total" value="{{ total }}"> </p> </form> Last value submitted: {{ value }}| Total:{{ total }} </body> </html> </code></pre> <p>The <code>index.html</code> view uses the dictionary keys <code>value</code> and <code>total</code> to show the result and to submit back the total to the controller using an <code>hidden</code> field.</p> <p>And here is the result:</p> <p><img src="https://i.stack.imgur.com/qbySR.png" alt="enter image description here"></p>

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