“Python Singleton Module” Ответ

Python Singleton

class Singleton:
    """
    A non-thread-safe helper class to ease implementing singletons.
    This should be used as a decorator -- not a metaclass -- to the
    class that should be a singleton.

    The decorated class can define one `__init__` function that
    takes only the `self` argument. Also, the decorated class cannot be
    inherited from. Other than that, there are no restrictions that apply
    to the decorated class.

    To get the singleton instance, use the `instance` method. Trying
    to use `__call__` will result in a `TypeError` being raised.

    """

    def __init__(self, decorated):
        self._decorated = decorated

    def instance(self):
        """
        Returns the singleton instance. Upon its first call, it creates a
        new instance of the decorated class and calls its `__init__` method.
        On all subsequent calls, the already created instance is returned.

        """
        try:
            return self._instance
        except AttributeError:
            self._instance = self._decorated()
            return self._instance

    def __call__(self):
        raise TypeError('Singletons must be accessed through `instance()`.')

    def __instancecheck__(self, inst):
        return isinstance(inst, self._decorated)
Nervous Nightingale

Python Singleton Module

# mymodule.py

__all__ = ["mysingleton"]

class __MySingletonLike(object):
    def __init__(self):
        self._variable = 42

    @property
    def variable(self):
        return self._variable

    @variable.setter
    def variable(self, value):
        check_value(value) # imaginary validation
        self._variable = value


mysingleton = __MySingleton()
T

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