'Get a single assignment details between a host and a volume.'

def get_single_assignment(self, vol, host, raise_on_non_exists=True):

    for assign in self.list_assignments(vol=vol):
        if (assign['host'] == host):
            return assign
    if raise_on_non_exists:
        raise exception.RdxAPICommandException((_('No    such    assignment    vol:%(vol)s,    host:%(host)s') % {'vol': vol, 'host': host}))
    else:
        return None
