def relativeScope(fromScope, destScope):
    """relativeScope(fromScope, destScope) -> list

Given two globally-scoped names, return a minimal scoped name list
which identifies the destination scope, without clashing with another
identifier. For example, given IDL:

  module M {
    typedef short A;
    typedef long  B;

    module N {
      typedef string B;
      interface I {
        void op(in ::M::A x, in ::M::B y);
      };
    };
  };

relativeScope(["M", "N", "I"], ["M", "A"]) -> ["A"]
relativeScope(["M", "N", "I"], ["M", "B"]) -> ["M", "B"]

If the only valid result is a globally-scoped name, the result list is
prefixed with None:

  module O {
    typedef short C;
  };
  module P {
    module O {
      interface J {
        void op(in ::O::C z);
      };
    };
  };

relativeScope(["P", "O", "J"], ["O", "C"]) -> [None, "O", "C"]
"""
    if not fromScope:
        return destScope
    import _omniidl
    rs = _omniidl.relativeScopedName(fromScope, destScope)
    if rs is None:
        return [None] + destScope
    else:
        return rs
