Python - 将对象的属性复制到另一个的正确方法是什么？

Question

I have two classes. They're almost identical, except for 2 attributes. I need to copy all the attributes over from one to the other, and I'm just wondering if there is a pattern or best practice, or if I should just basically do:

spam.attribute_one = foo.attribute_one
spam.attribute_two = foo.attribute_two

... and so on.

Answer 1

The code you give is correct and safe, avoiding "accidentally" binding attributes that should not be bound. If you favor automation over safety and correctness, though, you could use something like...:

def blindcopy(objfrom, objto):
    for n, v in inspect.getmembers(objfrom):
        setattr(objto, n, v);

However, I would not recommend it (for the reasons implied by the first para;-). OTOH, if you know the names of the attributes you want to copy, the following is just fine:

def copysome(objfrom, objto, names):
    for n in names:
        if hasattr(objfrom, n):
            v = getattr(objfrom, n)
            setattr(objto, n, v);

If you do this kind of thing often, having this code once in a "utilities" module can be a definite win for you!

Answer 2

If they're that similar, and need to change state, it sounds like you really have instances of one class, and a mode or similar attribute that determines how it behaves. Objects shouldn't morph from one object to another, similar but separate object, very often at all.

Answer 3

I used dictionary comprehension to iterate through the items and call setattr() for another object.

{k: setattr(object_to, k, v) for k, v in object_from.dict().items()}

Since I don't need any new dict , I have not assigned the return value to any variable.

Another way I tried is by using map()

dict(
    map(lambda item: (item[0], setattr(object_to, item[0], item[1])
                      ),
        object_from.dict().items()
        )
)

This might save a lot of loop iteration time.