1#!/usr/bin/env python3 2# Copyright 2023 - The Android Open Source Project 3# 4# Licensed under the Apache License, Version 2.0 (the "License"); 5# you may not use this file except in compliance with the License. 6# You may obtain a copy of the License at 7# 8# http://www.apache.org/licenses/LICENSE-2.0 9# 10# Unless required by applicable law or agreed to in writing, software 11# distributed under the License is distributed on an "AS IS" BASIS, 12# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13# See the License for the specific language governing permissions and 14# limitations under the License. 15 16"""A meta class for singleton pattern. 17 18Usage: 19 from atest.tools.singleton import Singleton 20 21 class AClass(BaseClass, metaclass=Singleton): 22 pass 23""" 24 25 26class Singleton(type): 27 """A singleton metaclass that returns the same instance when called.""" 28 29 _instances = {} 30 31 def __call__(cls, *args, **kwds): 32 """Initialize a singleton instance.""" 33 if cls not in cls._instances: 34 cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwds) 35 return cls._instances[cls] 36