如何获取除魔术方法/属性之外的已定义类属性的dict？

Question

Basically, what I am doing is

class A(object):
    a = 1
    b = 2

copy.deepcopy(dict(A.__dict__))

It gives the error

TypeError: object. new (getset_descriptor) is not safe, use getset_descriptor. new ()

If I update code like below one and pop out __dict__ and __weakref __ from class dictionary items

class A(object):
    a = 1
    b = 2

attrs = dict(A.__dict__)
attrs.pop("__weakref__")
attrs.pop("__dict__")
copy.deepcopy(dict(A.__dict__))
# It gives {'__module__': '__main__', 'a': 1, 'b': 2, '__doc__': None}

It works fine, I understand this is something related to copying weakref which will be wrong.

Is there any better way of doing the same where I don't need to specifically pop out __dict__ and __weakref __ and I can get only attributes of the Class, exclusive of magic methods/attributes?

Answer 1

It's not really that simple in Python, since there often isn't any way to know what's "built-in" and what's not. Also, using __dict__ isn't sufficient if you want to get inherited attributes; for that, you'd need to use dir instead, which conveniently also handles instances of objects the same as it'd handle classes themselves, and is thus more general purpose.

The simplest general-purpose solution would be to define yourself a simple little function that encapsulates what you want in terms of "attributes". You can then explicitly remove attributes you don't want to keep around (though, notice that if you deep copy such a filtered object, you probably won't have a usable Python object anymore):

In [1]: {k: getattr(A, k) for k in set(dir(A)) - set(dir(object)) - {'__weakref__', '__dict__', '__module__'}}
Out[1]: {'b': 2, 'a': 1}

In [2]: class B(A):
    ...:     c = 10

In [3]: {k: getattr(B, k) for k in set(dir(B)) - set(dir(object)) - {'__weakref__', '__dict__', '__module__'}}
Out[3]: {'b': 2, 'c': 10, 'a': 1}