对UserDict的研究

# -*- coding: utf-8 -*-
#python 27
#xiaodeng
#对UserDict的研究

class UserDict():
    def __init__(self, dict=None, **kwargs):
        self.data = {}  #定义self.data
        if dict is not None:
            self.update(dict)
        if len(kwargs):
            self.update(kwargs)
        #print self.data  #构造函数

    def __repr__(self):#有该语句，a=UserDict(b)，print a时，可打印实例内容
        return repr(self.data) 

    def __cmp__(self, dict):
        if isinstance(dict, UserDict):
            return cmp(self.data, dict.data)
        else:
            return cmp(self.data, dict)
    __hash__ = None # Avoid Py3k warning

    def __len__(self):
        '''
        给类构造长度运算方式，当a=UserDict(b)实例化时，print len(a)才能有运算结果
        没有__len__语句，会报错，
        如：AttributeError: UserDict instance has no attribute '__len__'
        提示说明：UserDict instance(UserDict实例)没有__len__属性
        '''
        return len(self.data)

    def __getitem__(self, key):
        if key in self.data:
            return self.data[key]
        if hasattr(self.__class__, "__missing__"):
            return self.__class__.__missing__(self, key)
        raise KeyError(key)

    def __setitem__(self, key, item):
        '''
        #__setitem__，不需要返回值，所以没有return
        #怎么调用？
        #a['a']=5
        '''
        self.data[key] = item

    #__delitem__，不需要返回值，所以没有return
    def __delitem__(self, key):
        '调用方式：del a[key]'
        del self.data[key]

    def clear(self): self.data.clear()

    def copy(self):
        if self.__class__ is UserDict:
            return UserDict(self.data.copy())
        import copy
        data = self.data
        try:
            self.data = {}
            c = copy.copy(self)
        finally:
            self.data = data
        c.update(self)
        return c

    def keys(self):
        '''
        >>> a.keys() #key键
        ['age', 'name', 'laiYuan']
        '''
        return self.data.keys()#注意data不能省略

    def items(self):
        return self.data.items()

    def iteritems(self):
        return self.data.iteritems()

    def iterkeys(self):
        return self.data.iterkeys()

    def itervalues(self):
        return self.data.itervalues()

    def values(self):
        '''
        >>> a.values()
        [28, 'xiaodeng', 'hubei']
        '''
        return self.data.values()
    def has_key(self, key): return key in self.data

    #更新操作
    def update(self, dict=None, **kwargs):
        if dict is None:
            pass
        elif isinstance(dict, UserDict):
            self.data.update(dict.data)
        elif isinstance(dict, type({})) or not hasattr(dict, 'items'):
            self.data.update(dict)
        else:
            for k, v in dict.items():
                self[k] = v
        if len(kwargs):
            self.data.update(kwargs)

    def get(self, key, failobj=None):
        '''
        failobj：预定义内容，
        该段小代码的意思是key是否在self中，如果不存在，则返回failobj，如存在可返回其value值
        print a.get('name')#failobj用预定义的值None
        print a.get('YuYan','python')
        '''
        if key not in self:
            return failobj
        return self[key]

    def setdefault(self, key, failobj=None):
        '与get有异曲同工之妙'
        if key not in self:
            self[key] = failobj
        return self[key]

    def pop(self, key, *args):
        return self.data.pop(key, *args)

    def popitem(self):
        '删除并返回dict中任意的一个(key,value)队，如果字典为空会抛出KeyError'
        'KeyError:popitem(): dictionary is empty'
        return self.data.popitem()

    def __contains__(self, key):
        return key in self.data
    @classmethod
    def fromkeys(cls, iterable, value=None):
        d = cls()
        for key in iterable:
            d[key] = value
        return d
if __name__=='__main__':
    b={'name':'xiaodeng','age':28,'laiYuan':'hubei'}
    a=UserDict(b)
    print a
    print len(a)
    print a.get('name')
    print a.get('bb','python')