Limits inventory results to a subset of inventory that matches a given
        pattern, such as to select a given geographic of numeric slice amongst
        a previous 'hosts' selection that only select roles, or vice versa.  
        Corresponds to --limit parameter to ansible-playbook

def subset(self, subset_pattern):
        """ 
        Limits inventory results to a subset of inventory that matches a given
        pattern, such as to select a given geographic of numeric slice amongst
        a previous 'hosts' selection that only select roles, or vice versa.  
        Corresponds to --limit parameter to ansible-playbook
        """        
        if subset_pattern is None:
            self._subset = None
        else:
            subset_pattern = subset_pattern.replace(',',':')
            self._subset = subset_pattern.replace(";",":").split(":")