docs: def get_class_alias(klass_or_alias):
      """
      Finds the L{ClassAlias} that is registered to C{klass_or_alias}.
  
      If a string is supplied and no related L{ClassAlias} is found, the alias is
      loaded via L{load_class}.
  
      @raise UnknownClassAlias: Unknown alias
      """
      if isinstance(klass_or_alias, python.str_types):
          try:
              return CLASS_CACHE[klass_or_alias]
          except KeyError:
              return load_class(klass_or_alias)
  
      try:
          return CLASS_CACHE[klass_or_alias]
      except KeyError:
          raise UnknownClassAlias('Unknown alias for %r' % (klass_or_alias,))