#!/usr/bin/env python
# -*- encoding: utf-8 -*-
"""
Topic: 混入类
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。
    Mixin也是多继承的主要用途。
"""


class LoggedMappingMixin:
    """
    Add logging to get/set/delete operations for debugging.
    """
    __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

    def __getitem__(self, key):
        print('Getting ' + str(key))
        return super().__getitem__(key)

    def __setitem__(self, key, value):
        print('Setting {} = {!r}'.format(key, value))
        return super().__setitem__(key, value)

    def __delitem__(self, key):
        print('Deleting ' + str(key))
        return super().__delitem__(key)


class SetOnceMappingMixin:
    '''
    Only allow a key to be set once.
    '''
    __slots__ = ()

    def __setitem__(self, key, value):
        if key in self:
            raise KeyError(str(key) + ' already set')
        return super().__setitem__(key, value)


class StringKeysMappingMixin:
    '''
    Restrict keys to strings only
    '''
    __slots__ = ()

    def __setitem__(self, key, value):
        if not isinstance(key, str):
            raise TypeError('keys must be strings')
        return super().__setitem__(key, value)


class LoggedDict(LoggedMappingMixin, dict):
    pass


d = LoggedDict()
d['x'] = 23
print(d['x'])
del d['x']

from collections import defaultdict


class SetOnceDefaultDict(SetOnceMappingMixin, defaultdict):
    pass


d = SetOnceDefaultDict(list)
d['x'].append(2)
d['x'].append(3)
# d['x'] = 23  # KeyError: 'x already set'


def LoggedMapping(cls):
    """第二种方式：使用类装饰器"""
    cls_getitem = cls.__getitem__
    cls_setitem = cls.__setitem__
    cls_delitem = cls.__delitem__

    def __getitem__(self, key):
        print('Getting ' + str(key))
        return cls_getitem(self, key)

    def __setitem__(self, key, value):
        print('Setting {} = {!r}'.format(key, value))
        return cls_setitem(self, key, value)

    def __delitem__(self, key):
        print('Deleting ' + str(key))
        return cls_delitem(self, key)

    cls.__getitem__ = __getitem__
    cls.__setitem__ = __setitem__
    cls.__delitem__ = __delitem__
    return cls


@LoggedMapping
class LoggedDict(dict):
    pass