102 lines
2.3 KiB
Python
102 lines
2.3 KiB
Python
#!/usr/bin/env python
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# -*- encoding: utf-8 -*-
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"""
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Topic: 混入类
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Desc : 如果单独使用Minxin类没有任何意义，但是当利用多继承和其他类配合后就有神奇效果了。
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Mixin也是多继承的主要用途。
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"""
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class LoggedMappingMixin:
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"""
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Add logging to get/set/delete operations for debugging.
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"""
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__slots__ = () # 混入类都没有实例变量，因为直接实例化混入类没有任何意义
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def __getitem__(self, key):
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print('Getting ' + str(key))
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return super().__getitem__(key)
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def __setitem__(self, key, value):
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print('Setting {} = {!r}'.format(key, value))
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return super().__setitem__(key, value)
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def __delitem__(self, key):
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print('Deleting ' + str(key))
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return super().__delitem__(key)
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class SetOnceMappingMixin:
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'''
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Only allow a key to be set once.
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'''
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__slots__ = ()
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def __setitem__(self, key, value):
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if key in self:
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raise KeyError(str(key) + ' already set')
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return super().__setitem__(key, value)
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class StringKeysMappingMixin:
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'''
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Restrict keys to strings only
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'''
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__slots__ = ()
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def __setitem__(self, key, value):
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if not isinstance(key, str):
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raise TypeError('keys must be strings')
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return super().__setitem__(key, value)
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class LoggedDict(LoggedMappingMixin, dict):
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pass
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d = LoggedDict()
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d['x'] = 23
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print(d['x'])
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del d['x']
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from collections import defaultdict
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class SetOnceDefaultDict(SetOnceMappingMixin, defaultdict):
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pass
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d = SetOnceDefaultDict(list)
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d['x'].append(2)
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d['x'].append(3)
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# d['x'] = 23 # KeyError: 'x already set'
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def LoggedMapping(cls):
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"""第二种方式：使用类装饰器"""
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cls_getitem = cls.__getitem__
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cls_setitem = cls.__setitem__
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cls_delitem = cls.__delitem__
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def __getitem__(self, key):
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print('Getting ' + str(key))
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return cls_getitem(self, key)
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def __setitem__(self, key, value):
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print('Setting {} = {!r}'.format(key, value))
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return cls_setitem(self, key, value)
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def __delitem__(self, key):
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print('Deleting ' + str(key))
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return cls_delitem(self, key)
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cls.__getitem__ = __getitem__
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cls.__setitem__ = __setitem__
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cls.__delitem__ = __delitem__
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return cls
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@LoggedMapping
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class LoggedDict(dict):
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pass
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