code: def resolve_class(classref):
      
      if classref is None:
          return None
      elif isinstance(classref, six.class_types):
          return classref
      elif isinstance(classref, six.string_types):
          return import_class(classref)
      else:
          raise ValueError("Unable to resolve class for '%s'" % classref)
docs: Attempt to return a Python class for the input class reference.
  
      If `classref` is a class or None, return it. If `classref` is a
      python classpath (e.g., "foo.bar.MyClass") import the class and return
      it.
  
      Args:
          classref: A fully-qualified Python path to class, or a Python class.
  
      Returns:
          A class.