I doubt it's an issue of Python community vs Ruby community. Instantiating arbitrary objects is the sort of feature I'd expect an object serialization library to have, but not a document serialization library. Pickle is clearly an object serialization library, and I would have naively assume that YAML is a document serialization format, but apparently either the authors of the Ruby YAML parser or the creators of YAML don't see it that way, and see YAML as an object serialization format that is by default permitted to specify arbitrary objects to instantiate.