关于`namedtuple`的一些内容在3.5.1中有所改变吗？

Question

在Python 3.5.0上:

>>> 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

似乎有些事情发生了namedtuple变化(或者可能是某些事情vars()？).

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？

Answer 1

每个Python bug#24931:

[ __dict__]消失了,因为它在Python 3中从根本上被破坏了,因此必须将其删除.提供__dict__破坏子类化并产生奇怪的行为.

进行更改的修订版

具体来说,没有__slots__定义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().

Answer 2

来自文档

命名的元组实例没有每个实例的字典,因此它们是轻量级的,并且不需要比常规元组更多的内存.

该 文档(和help(namedtuple))说,使用c._asdict()转换为一个字典.

Answer 3

__dict__被实施为@property已被删除; 你可以看到源代码的变化:

3.5.0:

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

3.5.1:

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)