Question

I am trying to copy all the methods and attributes from a class to an instance of another class. Unfortunately I am having issues with properties. Here’s an example:

class ToAdd(object):
    @property
    def foo(self):
        return 'foo!'

class Base(object):
    pass

b = Base()
for item, val in ToAdd.__dict__.iteritems():
    if not item.startswith('__'):
        setattr(b, item, val)

When calling b.foo I expect to get 'foo!', but instead it returns <property at 0x104a73d08>.

Note that this is akin to a mixin, but I want it to work on instances instead of classes.

Answer 1

There is probably a way to accomplish what you want with less “magic”, but it is possible to change an instance’s class…

class ToAdd(object):
    @property
    def foo(self):
        return 'foo!'

class Base(object):
    pass

b = Base()

NewBase = type('NewBase', (Base, ToAdd), {})
b.__class__ = NewBase
print(b.foo)
# foo!