CODEWITHSUNDEEP
pythondesign-patterns
orokusaki
orokusaki

Reputation: 57158

Python - what is the correct way to copy an object's attributes over to another?

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.

Upvotes: 15

Views: 11875

Answers (3)

Neisha
Neisha

Reputation: 11

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.

Upvotes: 0

Alex Martelli
Alex Martelli

Reputation: 882123

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!

Upvotes: 20

Peter
Peter

Reputation: 132307

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.

Upvotes: 3

Related Questions