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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 session_token(self):
 """Return OAuth session token."""

        session_token = None
        if self.user_id is not None:
            session_token = token_getter(self.remote)
        if session_token:
            token = RemoteToken.get(
                self.user_id, self.remote.consumer_key,
                access_token=session_token[0]
            )
            return token
        return None