code: def check_index(self, key, *, index):
          
          self.append({
              "Verb": "check-index",
              "Key": key,
              "Index": extract_attr(index, keys=["ModifyIndex", "Index"])
          })
          return self
docs: Fails the transaction if Key does not have a modify index equal to
          Index
  
          Parameters:
              key (str): Key to check
              index (ObjectIndex): Index ID