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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 to_string(self):
 """Returns this token as a plain string, suitable for storage. The resulting string includes the token's secret, so you should never send or store this string where a third party can read it. """

        items = [
            ('oauth_token', self.key),
            ('oauth_token_secret', self.secret),
        ]

        if self.callback_confirmed is not None:
            items.append(('oauth_callback_confirmed', self.callback_confirmed))
        return urlencode(items)