Decorate class methods dynamically raises error in python

Question

I am following this answer in order to decorate all methods of a class. This is my version of the code:

def decorate_object_methods(object_to_decorate, decorator):
    for name in dir(object_to_decorate):
        attr = getattr(object_to_decorate, name)
        if callable(attr):
            wrapped = decorator(attr)
            setattr(object_to_decorate, name, wrapped)

The problem is that I am getting this exception in the last sentence of the method:

TypeError: __class__ must be set to a class, not 'function' object

I can't find what I'm doing wrong