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36 lines
1.2 KiB
Python
36 lines
1.2 KiB
Python
class Singleton:
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"""
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A non-thread-safe helper class to ease implementing singletons.
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This should be used as a decorator -- not a metaclass -- to the
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class that should be a singleton.
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The decorated class can define one `__init__` function that
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takes only the `self` argument. Other than that, there are
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no restrictions that apply to the decorated class.
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To get the singleton instance, use the `Instance` method. Trying
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to use `__call__` will result in a `TypeError` being raised.
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Limitations: The decorated class cannot be inherited from.
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"""
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def __init__(self, decorated):
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self._decorated = decorated
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def Instance(self):
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"""
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Returns the singleton instance. Upon its first call, it creates a
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new instance of the decorated class and calls its `__init__` method.
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On all subsequent calls, the already created instance is returned.
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"""
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try:
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return self._instance
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except AttributeError:
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self._instance = self._decorated()
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return self._instance
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def __call__(self):
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raise TypeError('Singletons must be accessed through `Instance()`.')
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