是Python 3.5.0:
>>> from collections import namedtuple
>>> cluster = namedtuple('Cluster', ['a', 'b'])
>>> c = cluster(a=4, b=9)
>>> c
Cluster(a=4, b=9)
>>> vars(c)
OrderedDict([('a', 4), ('b', 9)])
在Python 3.5.1上:
>>> from collections import namedtuple
>>> cluster = namedtuple('Cluster', ['a', 'b'])
>>> c = cluster(a=4, b=9)
>>> c
Cluster(a=4, b=9)
>>> vars(c)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: vars() argument must have __dict__ attribute
似乎有关于namedtuple
改变的东西(或者它可能是关于vars()
的东西?)。
这是故意的吗?我们不应该使用这种模式将命名元组转换为字典吗?
[
__dict__
]消失了,因为它在Python 3中从根本上被破坏了,所以它必须被删除。提供__dict__
打破了子类并产生奇怪的行为。
具体来说,没有定义__slots__
的子类会表现得很奇怪:
>>> Cluster = namedtuple('Cluster', 'x y')
>>> class Cluster2(Cluster):
pass
>>> vars(Cluster(1,2))
OrderedDict([('x', 1), ('y', 2)])
>>> vars(Cluster2(1,2))
{}
使用._asdict()
。
__dict__
被实施为@property
并已被删除;你可以看到源代码的变化:
def __repr__(self):
'Return a nicely formatted representation string'
return self.__class__.__name__ + '({repr_fmt})' % self
@property
def __dict__(self):
'A new OrderedDict mapping field names to their values'
return OrderedDict(zip(self._fields, self))
def _asdict(self):
'Return a new OrderedDict which maps field names to their values.'
return self.__dict__
def __getnewargs__(self):
'Return self as a plain tuple. Used by copy and pickle.'
return tuple(self)
def __getstate__(self):
'Exclude the OrderedDict from pickling'
return None
def __repr__(self):
'Return a nicely formatted representation string'
return self.__class__.__name__ + '({repr_fmt})' % self
def _asdict(self):
'Return a new OrderedDict which maps field names to their values.'
return OrderedDict(zip(self._fields, self))
def __getnewargs__(self):
'Return self as a plain tuple. Used by copy and pickle.'
return tuple(self)