How to copy an uninitialized class in python

Question

I have this class

class TestEvent(object)
    value = None

I want to get a duplicate of this class so it isn't referenced but when i try using the copy library the variables are always referenced:

>>> clsOne = TestEvent
>>> clsTwo = copy.deepcopy(TestEvent)
>>> clsOne.value = "hello motto"
>>> clsTwo.value
"hello motto"

This is also the case with copy.copy. Can someone show me how to get a duplicate of this class?

Could you expand on the context - *why* do you need to create a copy of the class? — jonrsharpe, May 03 '18 at 21:42
For unit testing. I'm making a class inherited by `unittest.TestResult` to keep track of results in my own way. I want to be able to run multiple of these in using threads, but since this class is always referenced the results end up mixed up. — Kirk Douglas Jr, May 03 '18 at 21:44
But why are you storing attributes on the _class_, and not on _instances_? — Aran-Fey, May 03 '18 at 21:45
The example was just to the show the issue i'm having, unitttest create a new instance of the class but for some reason it's changes are being referenced back to the class itself. Something i'm not skilled enough to understand yet. — Kirk Douglas Jr, May 03 '18 at 21:57

Andrea Corbellini · Accepted Answer · 2018-05-03T21:58:14.387

2

copy.copy() and friends will return the value unchanged when you pass a class.

You can use type() instead:

# shallow copy of the namespace
new_cls = type(cls.__name__, cls.__bases__, dict(cls.__dict__))

or:

# deep copy of the namespace
new_cls = type(cls.__name__, cls.__bases__, copy.deepcopy(dict(cls.__dict__)))

edited May 03 '18 at 21:58

answered May 03 '18 at 21:53

Andrea Corbellini

1 Answers1