如何将对象.__ dict__再次转换为对象本身？

Question

class Node(object):
    def __init__(self, data):
        self.data = data

if __name__ == "__main__":
    a = Node(5)
    print a # prints __main__.Node object at 0x025C7530
    print a.__dict__ # how can I turn this back into the previous line?

无论如何将 dict 转回对象？

Answer 1

对于某些类型的对象，您可以获得相同的对象（不是对象本身，而是副本）：

class Node(object):
    def __init__(self, data):
        self.data = data

if __name__ == "__main__":
    a = Node(5)
    a = a.__dict__ #whoops, now I lost the object, I just have the dict
    b = Node.__new__(Node) # make a new empty object
    b.__dict__ = a.copy() # copy in the dict
    # copy because there might still a reference to the object elsewhere
    # if you want changes to b to affect a, then don't copy just assign
    print b.__dict__
    print b

Answer 2

严格地说，你不能（不修改Node类）。 __dict__不保留对原始对象的引用。您可以通过复制dict来完成类似的：

n1 = Node(5)
n2 = Node.__new__(Node) # object created but not initiated.
n2.__dict__ = n1.__dict__
n1.foo = 'something fooish'

print n1.foo == n2.foo #True

不幸的是，n1 != n2。

Answer 3

我只知道Python 2中的旧式类是可能的：

class Ode(): # not derived from object
    def __init__(self, data):
        self.data = data

>>> o = Ode(6)
>>> o.data
6

>>> import new
>>> od = o.__dict__
>>> od
{'data': 6}
>>> new.instance(Ode, od).data
6
>>> new.instance(Ode, {'data': 666}).data
666

但请注意，这与复制对象不同，我觉得你可能会遇到各种奇怪的问题（仅举一例：没有调用对象的构造函数）。