如何使用上下文管理器例外

Question

I need to read file attachments from email messages. I wanted to use context manager for resource management (connection should be closed)

@contextmanager
def some_f():
    conn = None
    try:
        for _ in xrange(CONNECTION_ERRORS_MAX):
            try:
                conn = POP3(self.pop3_host)
                conn.user(self.pop3_user)
                conn.pass_(self.pop3_password)
                logger.debug('connected {}', conn.getwelcome())
                _, msg_ids, _ = conn.uidl()
                yield (
                    (msg_id, self.files_from_msg(conn, file_batch_id, msg_id))
                    for msg_id, file_batch_id in
                    (ul.split(' ') for ul in msg_ids)
                    if not self.is_ignored(file_batch_id, msg_id)
                )
            except socket.error as e:
                if e.errno == errno.ECONNREFUSED:
                    pass
                else:
                    raise e
    finally:
        if conn:
            conn.quit()

So what this function supposed to do is try to connect to a email server, retry n-times if connection was refused if another socket error have happened then reraise it. If retry attempts are exhausted then reraise connection refused error. After the consumer would consume all files close connection. Right now it gives generator didn't yield error.

Answer 1

Restructure your try-except clause so that it surrounds the minimum number of things. In the except clause, you can continue if necessary, and if it is not triggered, you should break from the for loop.