Well. If python is a dynamically scoped language, what they do is correct. If they are lexically scoped (which python is described as) the variable defined in the if should never have different visibility in the same scope.

In a lexically scoped language you don't define variables conditionally. What ruby does is also icky, but obviously the developers of both python and ruby wanted to save the developer an extra declaration. The ruby version is at least more correct from a lexical standpoint (it is set to nil if left "nondefined").