'Return the region to use for listing resources.
:param  region: A name, region object, None, or \'all\'
:type   region: ``str`` or :class:`GCERegion` or ``None``
:return:  A region object or None if all regions should be considered
:rtype:   :class:`GCERegion` or ``None``'

def _set_region(self, region):

    region = (region or self.region)
    if ((region == 'all') or (region is None)):
        return None
    if (not hasattr(region, 'name')):
        region = self.ex_get_region(region)
    return region
