相关疑难解决方法(0)

理解与范围界定有一些意想不到的相互作用.这是预期的行为吗？

我有一个方法:

def leave_room(self, uid):
  u = self.user_by_id(uid)
  r = self.rooms[u.rid]

  other_uids = [ouid for ouid in r.users_by_id.keys() if ouid != u.uid]
  other_us = [self.user_by_id(uid) for uid in other_uids]

  r.remove_user(uid) # OOPS! uid has been re-bound by the list comprehension above

  # Interestingly, it's rebound to the last uid in the list, so the error only shows
  # up when len > 1

冒着抱怨的风险,这是一个残酷的错误来源.当我编写新代码时,我偶尔会发现由于重新绑定而导致非常奇怪的错误 - 即使现在我知道这是一个问题.我需要制定一个规则,比如"总是用下划线列出列表推导中的临时变量",但即使这样也不是万无一失的.

这种随机定时炸弹等待的事实否定了列表理解的所有"易用性".