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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_at_from_session(self):
 """ Get the saved access token for private resources from the session. """

        try:
            return self.request.session['oauth_%s_access_token'
                                        % get_token_prefix(
                                            self.request_token_url)]
        except KeyError:
            raise OAuthError(
                _('No access token saved for "%s".')
                % get_token_prefix(self.request_token_url))