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annotate rhodecode/lib/dbmigrate/migrate/versioning/util/keyedinstance.py @ 1976:a76e9bacbedc beta

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garden - unified logging formatting to use only %
author Marcin Kuzminski <marcin@python-works.com>
date Thu, 02 Feb 2012 00:31:00 +0200
parents 6832ef664673
children
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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)]