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40 lines
1.2 KiB
40 lines
1.2 KiB
4 months ago
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#!/usr/bin/env python3
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# Copyright 2019 - The Android Open Source Project
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""A meta class for singleton pattern."""
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class Singleton(type):
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"""A singleton metaclass.
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Class attributes:
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_instances: A dictionary keeps singletons' information, whose key is
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class and value is an instance of that class.
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Usage:
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from aidegen.lib import singleton
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class AClass(BaseClass, metaclass=singleton.Singleton):
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pass
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"""
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_instances = {}
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def __call__(cls, *args, **kwds):
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"""Initialize a singleton instance."""
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if cls not in cls._instances:
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cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwds)
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return cls._instances[cls]
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