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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 namespaces(**kwargs):
    '''
    Return the names of the available namespaces

    CLI Examples::

        salt '*' kubernetes.namespaces
        salt '*' kubernetes.namespaces kubeconfig=/etc/salt/k8s/kubeconfig context=minikube
    '''
    cfg = _setup_conn(**kwargs)
    try:
        api_instance = kubernetes.client.CoreV1Api()
        api_response = api_instance.list_namespace()

        return [nms['metadata']['name'] for nms in api_response.to_dict().get('items')]
    except (ApiException, HTTPError) as exc:
        if isinstance(exc, ApiException) and exc.status == 404:
            return None
        else:
            log.exception('Exception when calling CoreV1Api->list_namespace')
            raise CommandExecutionError(exc)
    finally:
        _cleanup(**cfg)