def metadefs_namespace_list(request,
                            filters=None,
                            sort_dir='asc',
                            sort_key='namespace',
                            marker=None,
                            paginate=False):
    """Retrieve a listing of Namespaces

    :param paginate: If true will perform pagination based on settings.
    :param marker: Specifies the namespace of the last-seen namespace.
             The typical pattern of limit and marker is to make an
             initial limited request and then to use the last
             namespace from the response as the marker parameter
             in a subsequent limited request. With paginate, limit
             is automatically set.
    :param sort_dir: The sort direction ('asc' or 'desc').
    :param sort_key: The field to sort on (for example, 'created_at'). Default
             is namespace. The way base namespaces are loaded into glance
             typically at first deployment is done in a single transaction
             giving them a potentially unpredictable sort result when using
             create_at.
    :param filters: specifies addition fields to filter on such as
             resource_types.
    :returns A tuple of three values:
        1) Current page results
        2) A boolean of whether or not there are previous page(s).
        3) A boolean of whether or not there are more page(s).

    """
    # Listing namespaces requires the v2 API. If not supported we return an
    # empty array so callers don't need to worry about version checking.
    if get_version() < 2:
        return [], False, False

    if filters is None:
        filters = {}
    limit = getattr(settings, 'API_RESULT_LIMIT', 1000)
    page_size = utils.get_page_size(request)

    if paginate:
        request_size = page_size + 1
    else:
        request_size = limit

    kwargs = {'filters': filters}
    if marker:
        kwargs['marker'] = marker
    kwargs['sort_dir'] = sort_dir
    kwargs['sort_key'] = sort_key

    namespaces_iter = glanceclient(request, '2').metadefs_namespace.list(
        page_size=request_size, limit=limit, **kwargs)

    # Filter the namespaces based on the provided properties_target since this
    # is not supported by the metadata namespaces API.
    resource_types = filters.get('resource_types')
    properties_target = filters.get('properties_target')
    if resource_types and properties_target:
        namespaces_iter = filter_properties_target(namespaces_iter,
                                                   resource_types,
                                                   properties_target)

    has_prev_data = False
    has_more_data = False
    if paginate:
        namespaces = list(itertools.islice(namespaces_iter, request_size))
        # first and middle page condition
        if len(namespaces) > page_size:
            namespaces.pop(-1)
            has_more_data = True
            # middle page condition
            if marker is not None:
                has_prev_data = True
        # first page condition when reached via prev back
        elif sort_dir == 'desc' and marker is not None:
            has_more_data = True
        # last page condition
        elif marker is not None:
            has_prev_data = True
    else:
        namespaces = list(namespaces_iter)

    namespaces = [Namespace(namespace) for namespace in namespaces]
    return namespaces, has_more_data, has_prev_data
Retrieve a listing of Namespaces

    :param paginate: If true will perform pagination based on settings.
    :param marker: Specifies the namespace of the last-seen namespace.
             The typical pattern of limit and marker is to make an
             initial limited request and then to use the last
             namespace from the response as the marker parameter
             in a subsequent limited request. With paginate, limit
             is automatically set.
    :param sort_dir: The sort direction ('asc' or 'desc').
    :param sort_key: The field to sort on (for example, 'created_at'). Default
             is namespace. The way base namespaces are loaded into glance
             typically at first deployment is done in a single transaction
             giving them a potentially unpredictable sort result when using
             create_at.
    :param filters: specifies addition fields to filter on such as
             resource_types.
    :returns A tuple of three values:
        1) Current page results
        2) A boolean of whether or not there are previous page(s).
        3) A boolean of whether or not there are more page(s).