Python 为什么我的班级没有';钥匙';功能?
谢谢Python 为什么我的班级没有';钥匙';功能?,python,inheritance,Python,Inheritance,谢谢 编辑:下面的类也不扩展任何类; 为什么它可以使用键 class a(object): w='www' def __init__(self): for i in self.keys(): print i def __iter__(self): for k in self.keys(): yield k a() # why is there an error here?
编辑:下面的类也不扩展任何类; 为什么它可以使用
键
class a(object):
w='www'
def __init__(self):
for i in self.keys():
print i
def __iter__(self):
for k in self.keys():
yield k
a() # why is there an error here?
为什么您希望它有
键
?您没有在类中定义这样的方法。你打算继承一本字典吗
为此,声明类a(dict)
或者你的意思是a.\u dict\u.keys()
对于您在更新中发布的大片段,请再次阅读类上方的注释:
class DictMixin:
# Mixin defining all dictionary methods for classes that already have
# a minimum dictionary interface including getitem, setitem, delitem,
# and keys. Without knowledge of the subclass constructor, the mixin
# does not define __init__() or copy(). In addition to the four base
# methods, progressively more efficiency comes with defining
# __contains__(), __iter__(), and iteritems().
# second level definitions support higher levels
def __iter__(self):
for k in self.keys():
yield k
def has_key(self, key):
try:
value = self[key]
except KeyError:
return False
return True
def __contains__(self, key):
return self.has_key(key)
# third level takes advantage of second level definitions
def iteritems(self):
for k in self:
yield (k, self[k])
def iterkeys(self):
return self.__iter__()
# fourth level uses definitions from lower levels
def itervalues(self):
for _, v in self.iteritems():
yield v
def values(self):
return [v for _, v in self.iteritems()]
def items(self):
return list(self.iteritems())
def clear(self):
for key in self.keys():
del self[key]
def setdefault(self, key, default=None):
try:
return self[key]
except KeyError:
self[key] = default
return default
def pop(self, key, *args):
if len(args) > 1:
raise TypeError, "pop expected at most 2 arguments, got "\
+ repr(1 + len(args))
try:
value = self[key]
except KeyError:
if args:
return args[0]
raise
del self[key]
return value
def popitem(self):
try:
k, v = self.iteritems().next()
except StopIteration:
raise KeyError, 'container is empty'
del self[k]
return (k, v)
def update(self, other=None, **kwargs):
# Make progressively weaker assumptions about "other"
if other is None:
pass
elif hasattr(other, 'iteritems'): # iteritems saves memory and lookups
for k, v in other.iteritems():
self[k] = v
elif hasattr(other, 'keys'):
for k in other.keys():
self[k] = other[k]
else:
for k, v in other:
self[k] = v
if kwargs:
self.update(kwargs)
def get(self, key, default=None):
try:
return self[key]
except KeyError:
return default
def __repr__(self):
return repr(dict(self.iteritems()))
def __cmp__(self, other):
if other is None:
return 1
if isinstance(other, DictMixin):
other = dict(other.iteritems())
return cmp(dict(self.iteritems()), other)
def __len__(self):
return len(self.keys())
请注意,“已经有…键”部分
DictMixin
类来自UserDict
模块,该模块表示:
类UserDict.DictMixin Mixin
定义的所有字典方法
已具有最小值的类
字典接口,包括
getitem()、setitem()、delitem()和keys()
这种混合物应作为一种添加剂使用
超类。添加上述各项
方法会逐渐增加更多
功能。例如,定义
除delitem外的所有文件都将排除
只有完整列表中的pop()和popitem()
接口
除了四种基本方法之外,
效率越来越高
通过定义包含(),
iter()和iteritems()
因为mixin不知道
子类构造函数,它没有
定义init()或copy()
从Python版本2.6开始,它
建议使用
collections.MutableMapping而不是
DictMixin
注意最后一部分中的建议-改用collections.MutableMapping
要迭代对象的属性,请执行以下操作:
# Mixin defining all dictionary methods for classes that already have
# a minimum dictionary interface including getitem, setitem, delitem,
# and keys
为什么您希望它有
键
?您没有在类中定义这样的方法。你打算继承一本字典吗
为此,声明类a(dict)
或者你的意思是a.\u dict\u.keys()
对于您在更新中发布的大片段,请再次阅读类上方的注释:
class DictMixin:
# Mixin defining all dictionary methods for classes that already have
# a minimum dictionary interface including getitem, setitem, delitem,
# and keys. Without knowledge of the subclass constructor, the mixin
# does not define __init__() or copy(). In addition to the four base
# methods, progressively more efficiency comes with defining
# __contains__(), __iter__(), and iteritems().
# second level definitions support higher levels
def __iter__(self):
for k in self.keys():
yield k
def has_key(self, key):
try:
value = self[key]
except KeyError:
return False
return True
def __contains__(self, key):
return self.has_key(key)
# third level takes advantage of second level definitions
def iteritems(self):
for k in self:
yield (k, self[k])
def iterkeys(self):
return self.__iter__()
# fourth level uses definitions from lower levels
def itervalues(self):
for _, v in self.iteritems():
yield v
def values(self):
return [v for _, v in self.iteritems()]
def items(self):
return list(self.iteritems())
def clear(self):
for key in self.keys():
del self[key]
def setdefault(self, key, default=None):
try:
return self[key]
except KeyError:
self[key] = default
return default
def pop(self, key, *args):
if len(args) > 1:
raise TypeError, "pop expected at most 2 arguments, got "\
+ repr(1 + len(args))
try:
value = self[key]
except KeyError:
if args:
return args[0]
raise
del self[key]
return value
def popitem(self):
try:
k, v = self.iteritems().next()
except StopIteration:
raise KeyError, 'container is empty'
del self[k]
return (k, v)
def update(self, other=None, **kwargs):
# Make progressively weaker assumptions about "other"
if other is None:
pass
elif hasattr(other, 'iteritems'): # iteritems saves memory and lookups
for k, v in other.iteritems():
self[k] = v
elif hasattr(other, 'keys'):
for k in other.keys():
self[k] = other[k]
else:
for k, v in other:
self[k] = v
if kwargs:
self.update(kwargs)
def get(self, key, default=None):
try:
return self[key]
except KeyError:
return default
def __repr__(self):
return repr(dict(self.iteritems()))
def __cmp__(self, other):
if other is None:
return 1
if isinstance(other, DictMixin):
other = dict(other.iteritems())
return cmp(dict(self.iteritems()), other)
def __len__(self):
return len(self.keys())
请注意,“已经有…键”部分
DictMixin
类来自UserDict
模块,该模块表示:
类UserDict.DictMixin Mixin
定义的所有字典方法
已具有最小值的类
字典接口,包括
getitem()、setitem()、delitem()和keys()
这种混合物应作为一种添加剂使用
超类。添加上述各项
方法会逐渐增加更多
功能。例如,定义
除delitem外的所有文件都将排除
只有完整列表中的pop()和popitem()
接口
除了四种基本方法之外,
效率越来越高
通过定义包含(),
iter()和iteritems()
因为mixin不知道
子类构造函数,它没有
定义init()或copy()
从Python版本2.6开始,它
建议使用
collections.MutableMapping而不是
DictMixin
注意最后一部分中的建议-改用collections.MutableMapping
要迭代对象的属性,请执行以下操作:
# Mixin defining all dictionary methods for classes that already have
# a minimum dictionary interface including getitem, setitem, delitem,
# and keys
class A(object):
,根据PEP 8:我添加了一个关于迭代对象属性的注释class A(object):
,根据PEP 8:我添加了一个关于迭代对象属性的注释Google found两秒钟的工作,所有这些都解释了如何使用DictMixin-这只知道名称。我相信百度也可以很容易地为你找到这些网站。用谷歌搜索的两秒钟时间,所有这些都解释了如何使用DictMixin,而这只知道它的名字。我相信百度也可以很容易地为你找到这些网站。