Manually Clone/Copy an instance in Python

I know we have both c开发者_开发技巧opy and deepcopy inside the module copy, but I'd like to do it manually...

I started by playing a little with __dict__ object just to see how can I create instances setting the same attributes that the object to be copied have, and here's the result of my first test:

class A(object):
    def F(self):
        print "Test!"

a = A()
x = type('A', (object, ), dict(A.__dict__))
x.F()

When executed, the following error appeared:

TypeError: unbound method F() must be called with A instance as first argument (got nothing instead)

How could I implement a method/function in Python to clone/copy (recursively) an object?

To manually create a shallow copy of an instance of the user-defined class A, you can do

a = A()
b = object.__new__(A)
b.__dict__ = a.__dict__.copy()   # or dict(a.__dict__)

The call to object.__new__() creates a new instance without calling __init__().

Your code constructs a new type object rather than a new instance of A.

Implementing a deep copy is much more involved -- you would basically need to reimplement the whole copy and copyreg modules. They are written in Python -- just follow the links to see the source code.

Without answering your "clone/copy" question, your code have a small bug. My version of your code is:

class A(object):
    def f(self):
        print "Test!"

a = A()
a.f()

X = type('A', (object, ), dict(A.__dict__))
x = X()
x.f()