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')
无语言基础,自学python所做的各种笔记,欢迎大牛指点.