Python:无法腌制类型X，属性查找失败 [英] Python: Can't pickle type X, attribute lookup failed

问题描述

我正在尝试腌制namedtuple:

from collections import namedtuple
import cPickle

class Foo:

    Bar = namedtuple('Bar', ['x', 'y'])

    def baz(self):
        s = set()
        s.add(Foo.Bar(x=2, y=3))
        print cPickle.dumps(s)

if __name__ == '__main__':
    f = Foo()
    f.baz()

这将产生以下输出:

Traceback (most recent call last):
  File "scratch.py", line 15, in <module>
    f.baz()
  File "scratch.py", line 11, in baz
    print cPickle.dumps(s)
cPickle.PicklingError: Can't pickle <class '__main__.Bar'>: attribute lookup __main__.Bar failed

我做错了什么?问题Bar是Foo的成员吗? (将Bar的定义移到最高级别可以解决此问题，尽管我仍然很好奇为什么会发生这种情况.)

What am I doing wrong? Is the problem that Bar is a member of Foo? (Moving the definition of Bar to the top level solves the problem, although I'm still curious why this happens.)

推荐答案

是的，它是类成员这一事实是一个问题:

Yes, the fact that it's a class member is a problem:

>>> class Foo():
...     Bar = namedtuple('Bar', ['x','y'])
...     def baz(self):
...         b = Foo.Bar(x=2, y=3)
...         print(type(b))
...
>>> a = Foo()
>>> a.baz()
<class '__main__.Bar'>

问题在于，当namedtuple()返回类型对象时，它不知道将其分配给类成员的事实-因此，它告诉类型对象其类型名称应为__main__.Bar ，即使它确实应该是__main__.Foo.Bar.

The problem is that when namedtuple() returns a type object, it isn't aware of the fact that it's being assigned to a class member - and thus, it tells the type object that its type name should be __main__.Bar, even though it should really be __main__.Foo.Bar.

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