[btown]

Alternately, if you want to just delegate everything, you can subclass wrapt.ObjectProxy https://wrapt.readthedocs.io/en/latest/wrappers.html#object-...

Python is scary sometimes. If it looks like a duck and quacks like a duck and isinstance(duck), it might be an alien masquerading as a duck using metaclasses to accomplish these feats. But with this craziness comes the ability to make a transparent runtime proxy to just about anything in Python, and do so recursively e.g. to track all uses of an object hierarchy.

[bgschiller]

I think I'm confused. If you want to delegate _everything_, why not just actually use inheritance? Or even the object itself. What's an example of when you would want an ObjectProxy?

Definitely agree about metaclass magic being a blessing and a curse. That superdelegate library was fun to write and uses a metaclass to make the API pleasant.

[btown]

If you don't know what you're going to need to wrap (heck, it might be something with methods implemented with native code), but you want to override or intercept a certain subset of calls, then composition/delegation is really the only thing you can do. It's significantly more stable than trying to find the class of an arbitrary object at runtime, create a subclass of it, and try to copy the state of the original object.

For instance, I've seen instrumentation libraries monkey-patch database cursors with wrappers around those cursors, so the library can detect usage of the cursor without changing its behavior.

Django itself has a LazyObject class, which operates similarly to an ObjectProxy but only evaluates its wrapped initializer when one of its properties is accessed: https://docs.djangoproject.com/en/2.2/_modules/django/utils/...

And I'm using wrapt in a project (which I hope to open source) where, by recursively wrapping the return value of every __getitem__ and __getattr__ with a properly-bookkept proxy object, you can see what subgraph of a complicated object hierarchy was actually used by a function call (say, the rendering of a Django or Jinja template). Possibilities of such a transformation are endless!

[zmmmmm]

You don't have to sacrifice type safety, that's a python problem. Other languages (eg: Groovy) accomplish the same thing in a type-safe way (see @Delegate annotation [1]).

http://docs.groovy-lang.org/2.4.9/html/gapi/groovy/lang/Dele...

[skocznymroczny]

In D some of that can be done with a Proxy mixin https://dlang.org/phobos/std_typecons.html#Proxy