Completely wrap an object in Python

I am wanting to completely wrap an object so that all attribute and method requests get forwarded to the object it's wrapping, but also overriding any methods or variables that I want, as well as providing some of my own methods. This wrapper class should appear 100% as the existing class (isinstance must act as if it is actually the class), however subclassing in itself is not going to cut it, as I want to wrap an existing object. Is there some solution in Python to do this? I was thinking something along the lines of:

class ObjectWrapper(BaseClass):
    def __init__(self, baseObject):
        self.baseObject = baseObject

    def overriddenMethod(self):
        ...

    def myOwnMethod1(self):
        ...

    ...

    def __getattr__(self, attr):
        if attr in ['overriddenMethod', 'myOwnMethod1', 'myOwnMethod2', ...]
            # return the requested method
        else:
            return getattr(self.baseObject, attr)

But I'm not that familiar with overriding __getattr__, __setattr__ and __hasattr__, so I'm not sure how to get that right.