> I don't think that's true in general, or true of how other Python APIs work. For instance, many APIs return a "file-like object", and you can only do certain things on that object, depending on what the documentation says, or what EAFP gets you. Some file-like object don't support seek/tell, some don't support close, etc. I've seen plenty of walk-like-a-duck checks like this:

Yes, I'm fully aware duck-typing ;-)
But here, you're saying that "a duck has a beak, but it *may* have
legs, a tail, etc".
It's just looks wrong to me on so many levels.

Please bring this up on python-dev.