[3] | 1 | #!/usr/bin/env python |
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| 2 | # -*- coding: utf-8 -*- |
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| 3 | |
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| 4 | class KeyedInstance(object): |
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| 5 | """A class whose instances have a unique identifier of some sort |
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| 6 | No two instances with the same unique ID should exist - if we try to create |
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| 7 | a second instance, the first should be returned. |
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| 8 | """ |
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| 9 | |
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| 10 | _instances = dict() |
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| 11 | |
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| 12 | def __new__(cls, *p, **k): |
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| 13 | instances = cls._instances |
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| 14 | clskey = str(cls) |
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| 15 | if clskey not in instances: |
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| 16 | instances[clskey] = dict() |
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| 17 | instances = instances[clskey] |
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| 18 | |
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| 19 | key = cls._key(*p, **k) |
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| 20 | if key not in instances: |
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| 21 | instances[key] = super(KeyedInstance, cls).__new__(cls) |
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| 22 | return instances[key] |
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| 23 | |
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| 24 | @classmethod |
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| 25 | def _key(cls, *p, **k): |
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| 26 | """Given a unique identifier, return a dictionary key |
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| 27 | This should be overridden by child classes, to specify which parameters |
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| 28 | should determine an object's uniqueness |
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| 29 | """ |
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| 30 | raise NotImplementedError() |
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| 31 | |
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| 32 | @classmethod |
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| 33 | def clear(cls): |
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| 34 | # Allow cls.clear() as well as uniqueInstance.clear(cls) |
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| 35 | if str(cls) in cls._instances: |
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| 36 | del cls._instances[str(cls)] |
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