37 lines
1.2 KiB
Python
37 lines
1.2 KiB
Python
class KeyedInstance(object):
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"""A class whose instances have a unique identifier of some sort
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No two instances with the same unique ID should exist - if we try to create
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a second instance, the first should be returned.
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"""
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# _instances[class][instance]
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_instances=dict()
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def __new__(cls,*p,**k):
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instances = cls._instances
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clskey = str(cls)
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if clskey not in instances:
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instances[clskey] = dict()
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instances = instances[clskey]
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key = cls._key(*p,**k)
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if key not in instances:
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instances[key] = super(KeyedInstance,cls).__new__(cls,*p,**k)
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self = instances[key]
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return self
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@classmethod
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def _key(cls,*p,**k):
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"""Given a unique identifier, return a dictionary key
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This should be overridden by child classes, to specify which parameters
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should determine an object's uniqueness
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"""
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raise NotImplementedError()
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@classmethod
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def clear(cls,cls2=None):
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# Allow cls.clear() as well as niqueInstance.clear(cls)
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if cls2 is not None:
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cls=cls2
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if str(cls) in cls._instances:
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del cls._instances[str(cls)]
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