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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 request_token(self):
 """Create an OAuth request token for a valid client request. Defaults to /request_token. Invoked by client applications. """

        client_key = request.oauth.client_key
        realm = request.oauth.realm
        # TODO: fallback on default realm?
        callback = request.oauth.callback_uri
        request_token = generate_token(length=self.request_token_length[1])
        token_secret = generate_token(length=self.secret_length)
        self.save_request_token(client_key, request_token, callback,
            realm=realm, secret=token_secret)
        return urlencode([(u'oauth_token', request_token),
                          (u'oauth_token_secret', token_secret),
                          (u'oauth_callback_confirmed', u'true')])