Question

Continue语句应使用下一项重新开始循环，但是当我的代码中发生异常时，for循环会退出。

def Update():
  numberRemoved = 0
  for conn in connections:
    print("Starting for loop")
    try:
      print("First one")
      conn.send("up?".encode())
      reply = conn.recv(1024)
      if reply.decode().strip() != "yes":
        print("Recieved reply but clients response was different from expected...")
    except ConnectionResetError:
      print("It's down")
      connections.remove(conn)
      print("Removed the connection")
      numberRemoved += 1
      continue

此代码遍历套接字连接列表，并检查客户端是否仍在运行，但是即使有继续语句，每次发生异常时，for循环也会停止。我该如何解决？谢谢！

Answer 1

您从迭代的列表中删除内容。这使python感到困惑-不要这样做。您需要防止所有可能的异常-您只能捕获一种类型，其他所有类型都将终止程序。

修复，以便在遇到问题时进行修改，或者：

记住要删除的内容
遍历副本并从原始副本中删除（确保它是副本，而不只是指向相同数据的新名称

记住要删除的内容的代码：

def Update(connections):
    to_be_removed = []
    for conn in connections:
        print("Starting for loop")
        try:
            print("First one") # not only the first one, every one is printing first one
            conn.send("up?".encode())
            reply = conn.recv(1024)
            if reply.decode().strip() != "yes":
                print("Response was different from expected...")
        except ConnectionResetError:   # other errors will kill your program
            print("It's down")
            to_be_removed.append(conn)

            # there is no need to put a continue into your except block, because there
            # is no code after the except block that belongs into the loop and 
            # has to be skipped if the exception happens - continue is superflous

    # remove items from list after iterating it 
    for conn in to_be_removed:
        connections.remove(conn)

如果您有[1,2,3,4]的列表并在其上循环：

k = [1,2,3,4]
for i in k:
    print(i,k)
    k.remove(i)
    print(k)

你得到

(1, [1, 2, 3, 4])   # i is 1, the 1st  number in k
[2, 3, 4]           # 1 is removed, continuing with 2nd element of list
(3, [2, 3, 4])      # list got modified, 3 is the 2nd element
[2, 4]              # 3 is removed, continuing with 3rd element of list
                    # oh wait - no 3rd element - cool - we are done

即使使用continue语句发生异常时，For循环也会退出

1 个答案: