code: def clear(self, only_read=False):
          
          self.cache_items.clear()
          self.total_access_count = 0
          self.logger.debug('Cache clear operation is completed')
docs: >>> cache = Cache(log_level=logging.WARNING)
          >>> cache.put('a', 0)
          >>> cache.put('b', 1)
          >>> cache.size()
          2
          >>> cache.clear()
          >>> cache.size()
          0