def sign(self, path, api='public', method='GET', params={}, headers=None, body=None):
    raise NotSupported((self.id + ' sign() pure method must be redefined in derived classes'))
def sign(self, path, api='public', method='GET', params={}, headers=None, body=None):
    raise NotSupported((self.id + ' sign() pure method must be redefined in derived classes'))