为什么我可以 pickle typing.NamedTuple时不 pickle collections.namedtuple?我该如何 pickle NamedTuple

这段代码显示了到目前为止我已经尝试过的内容:

from collections import namedtuple
from typing import NamedTuple

PersonTyping = NamedTuple('PersonTyping', [('firstname',str),('lastname',str)])
PersonCollections = namedtuple('PersonCollections', ['firstname','lastname'])

pt = PersonTyping("John","Smith")
pc = PersonCollections("John","Smith")


import pickle
import traceback

try:
    with open('personTyping.pkl', 'wb') as f:
        pickle.dump(pt, f)
except:
    traceback.print_exc()
try:
    with open('personCollections.pkl', 'wb') as f:
        pickle.dump(pc, f)
except:
    traceback.print_exc()

在 shell 上输出:
$ python3 prova.py
Traceback (most recent call last):
  File "prova.py", line 16, in <module>
    pickle.dump(pt, f)
_pickle.PicklingError: Can't pickle <class 'typing.PersonTyping'>: attribute lookup PersonTyping on typing failed
$

最佳答案

这是一个错误。我已经打开了一张票:http://bugs.python.org/issue25665

问题在于,在创建类时, namedtuple 函数通过从调用框架的全局变量中查找__module__属性来设置其__name__属性。在这种情况下,调用者是typing.NamedTuple

result.__module__ = _sys._getframe(1).f_globals.get('__name__', '__main__')

因此,在这种情况下,最终将其设置为'typing'
>>> type(pt)
<class 'typing.PersonTyping'>  # this should be __main__.PersonTyping
>>> type(pc)
<class '__main__.PersonCollections'>
>>> import typing
>>> typing.NamedTuple.__globals__['__name__']
'typing'

修复:

代替这个, NamedTuple 函数应该自己设置它:
def NamedTuple(typename, fields):

    fields = [(n, t) for n, t in fields]
    cls = collections.namedtuple(typename, [n for n, t in fields])
    cls._field_types = dict(fields)
    try:
        cls.__module__ = sys._getframe(1).f_globals.get('__name__', '__main__')
    except (AttributeError, ValueError):
        pass
    return cls

现在,您还可以执行以下操作:
PersonTyping = NamedTuple('PersonTyping', [('firstname',str),('lastname',str)])
PersonTyping.__module__ = __name__

关于python - 为什么我可以 pickle collections.namedtuple的同时不 pickle type.NamedTuple?,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/33796490/

10-13 09:38