'Check to see if a group exists
:param group_name: string - the group to check
:param parent_name: string - the parent of group_name
:return: boolean - whether the group exists'

def _group_exists(self, group_name, parent_name):

    result = False
    if (group_name in self.group_dict):
        (group, parent) = self.group_dict[group_name]
        if ((parent_name is None) or (parent_name == parent.name)):
            result = True
    return result
