old_contents: from abc import ABC, abstractmethod
  
  
  class ClientBase(ABC):
      @abstractmethod
      def download(self):
          pass
  
      @abstractmethod
      def upload(self):
          pass
  
      @abstractmethod
      def execute_query(self):
          pass
  
      @abstractmethod
      def execute_long_running_query(self):
          pass
  
new_contents: from abc import ABCMeta, abstractmethod
  
  
  class ClientBase():
      __metaclass__ = ABCMeta
  
      @abstractmethod
      def download(self):
          pass
  
      @abstractmethod
      def upload(self):
          pass
  
      @abstractmethod
      def execute_query(self):
          pass
  
      @abstractmethod
      def execute_long_running_query(self):
          pass
  
subject: fix python 2.7 tests, 2nd try