I've been working on a programming language / interpreter, and I'd guess that in the beginning it was probably just easier to implement len() and other such com

I've been working on a programming language / interpreter, and I'd guess that in the beginning it was probably just easier to implement len() and other such common / generic functions this way. You can either implement a single function that handles the various types or you can add a method to each type, but the latter can be pretty tedious when you're implementing a bunch of functions / methods that operate on numerous types. I ran into this when I started implementing map() for a few builtin types and found myself duplicating the loop-over-items code and started thinking, "Hmm, I wonder if this is why Python implemented len(), map(), etc as functions instead of methods." Of course, you could implement an abstract class or equivalent for the generic aspects of len(), map(), etc, but then that gets pretty complex too. So, based on that, which to reiterate is just a guess, I don't think the decision is bizarre at all. It's just an implementation tradeoff. From a developer point of view, I slightly prefer method syntax for aesthetic reasons, but practically speaking it doesn't make any difference whether I type obj.len() or len(obj), and IMO neither is more or less object-oriented than the other (which is a common complaint about len() et al).