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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 create_volume(self, volume_name: str, driver_spec: str = None):
 """Create new docker volumes. Only the manager nodes can create a volume Args: volume_name (string):
 Name for the new docker volume driver_spec (string):
 Driver for the docker volume """

        # Default values
        if driver_spec:
            driver = driver_spec
        else:
            driver = 'local'

        # Raise an exception if we are not a manager
        if not self._manager:
            raise RuntimeError('Services can only be deleted '
                               'on swarm manager nodes')

        self._client.volumes.create(name=volume_name, driver=driver)