# BSD 3-Clause License
#
# Copyright (C) 2021 THL A29 Limited, a Tencent company.  All rights reserved.
#
# Redistribution and use in source and binary forms, with or without modification,
# are permitted provided that the following conditions are met:
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#  * Redistributions of source code must retain the above copyright notice, this
#    list of conditions and the following disclaimer.
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#  * Redistributions in binary form must reproduce the above copyright notice,
#    this list of conditions and the following disclaimer in the documentation
#    and/or other materials provided with the distribution.
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#  * Neither the name of the psutil authors nor the names of its contributors
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#    specific prior written permission.
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class SingletonMeta(type):
    """
    The Singleton class can be implemented in different ways in Python. Some
    possible methods include: base class, decorator, metaclass. We will use the
    metaclass because it is best suited for this purpose.
    """

    _instances = {}

    def __call__(cls, *args, **kwargs):
        """
        Possible changes to the value of the `__init__` argument do not affect
        the returned instance.
        """
        if cls not in cls._instances:
            instance = super().__call__(*args, **kwargs)
            cls._instances[cls] = instance
        return cls._instances[cls]
