code: def parse_annotation(code):
      
      module = ast.parse(code)
      assert type(module) is ast.Module, 'internal error #1'
      assert len(module.body) == 1, 'Annotation contains more than one expression'
      assert type(module.body[0]) is ast.Expr, 'Annotation is not expression'
      return module.body[0]
docs: Parse an annotation string.
      Return an AST Expr node.
      code: annotation string (excluding '@')