Copying an object in Python [duplicate]

Question

This question already has answers here:

How can I create a copy of an object in Python? (4 answers)

Closed 9 years ago.

I come from a javascript background and while working in Python recently I'm having a bit of trouble with what (in JS) I would have called objects.

I've created a class with an init function that works as expected:

class TestClass(object):
    def __init__(self,var1,var2,...):
        self.var1 = var1
        self.var2 = var2
        ...

It may be worth knowing at this point, most of the variables that will be passed in here are actually arrays.

Everything is awesome, I can create instances of this object at will and it works as expected. For background, I'm doing this:

def make_object(var1,var2,...):
    object = TestClass(var1,var2,...)
    return object
object1 = make_object(var1, var2,...)

var1, var2 and so on are all arrays which I will work on in-situ later. Later in the script I do this:

object2 = object1
object3 = object1

As the values stored in these objects are arrays, I use another variable (worked out in another part of the script) to reduce the arrays down to just the element I need:

object2.var1 = object2.var1[requiredIndex]
object2.var2 = object2.var2[requiredIndex]
...

I do this for each array in the object and it sorts the data out perfectly - it was only when I added object3 into the whole equation and ran a similar command on it, that I discovered these lines:

object3.var1 = object3.var1[requiredIndex]
object3.var2 = object3.var2[requiredindex]
...

... discovered these lines were operating on the data I'd already refined using the same commands on object2, which I have tested and found has also affected object1 so as far as I can tell the three object names are all just references to the same set of data.

I need object2 and object3 to be independent of each other (and ideally, independent of object1) so how do I go about this? I hope I've provided enough detail to fully explain my issue. Cheers in advance!

Answer 1

You are probably looking for copy.deepcopy

object2 = copy.deepcopy(object1)
object3 = copy.deepcopy(object1)

-> Now you have three independent objects with no shared data.