root/galaxy-central/eggs/sqlalchemy_migrate-0.5.4-py2.6.egg/migrate/versioning/util/keyedinstance.py

リビジョン 3, 1.1 KB (コミッタ: kohda, 14 年 前)

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