Reclassing an instance in Python

Question

I have a class that is provided to me by an external library. I have created a subclass of this class. I also have an instance of the original class.

I now want to t

Answer 1

Heheh, fun example.

"Reclassing" is pretty weird, at first glance. What about the 'copy constructor' approach? You can do this with the Reflection-like hasattr, getattr and setattr. This code will copy everything from one object to another, unless it already exists. If you don't want to copy methods, you can exclude them; see the commented if.

class Foo(object):
    def __init__(self):
        self.cow = 2
        self.moose = 6

class Bar(object):
    def __init__(self):
        self.cat = 2
        self.cow = 11

    def from_foo(foo):
        bar = Bar()
        attributes = dir(foo)
        for attr in attributes:
            if (hasattr(bar, attr)):
                break
            value = getattr(foo, attr)
            # if hasattr(value, '__call__'):
            #     break # skip callables (i.e. functions)
            setattr(bar, attr, value)

        return bar

All this reflection isn't pretty, but sometimes you need an ugly reflection machine to make cool stuff happen. ;)