def login(self, username=None, password=None, token=None):
        if self._cookie is not None:
            raise RuntimeError('already logged in')
        if username is not None:
            if password is None:
                raise ValueError('username provided but not password')
            if token is not None:
                raise ValueError('cannot specify both username and token')
            self.username = username
            self.password = password
        elif token is not None:
            self.token = token
        self._login()
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dataset/ETHPy150Open ravello/testmill/lib/testmill/ravello.py/RavelloClient.login