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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_action(self, action):
 """ Retrieve a descriptor for the named action. Caches descriptors for efficiency. """


        # If we don't have an action named that, bail out
        if action not in self.wsgi_actions:
            return None

        # Generate an ActionDescriptor if necessary
        if action not in self.wsgi_descriptors:
            self.wsgi_descriptors[action] = actions.ActionDescriptor(
                self.wsgi_actions[action],
                self.wsgi_extensions.get(action, []),
                self.wsgi_resp_type)

        # OK, return the method descriptor
        return self.wsgi_descriptors[action]