def _check_nonce(self, consumer, token, nonce):
        """Verify that the nonce is uniqueish."""
        nonce = self.data_store.lookup_nonce(consumer, token, nonce)
        if nonce:
            raise OAuthError('Nonce already used: %s' % str(nonce))
Verify that the nonce is uniqueish.
twitter/oauth.py