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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 user(self):
 """The current user. This property is cached in the ``_user`` attribute. """

        if self._user is not None:
            return self._user

        cert = self.transport.getPeerCertificate()
        self._user = user = userForCert(self.store, cert)
        return user