python - pika模块的使用中，如何动态的删除一个 durable=True 的持久化队列？

问题描述

问 题

比如某个队列 'rpc_queue' 是以前由其他python脚本创建的持久化队列，在rabbitmq中一直存在着。
在某次写脚本时，也申明了一个同名的队列，但不是持久化的，就会报错。
如果直接删除再创建，当然可以，像这样：

channel.queue_delete(queue='rpc_queue')
channel.queue_declare(queue='rpc_queue')

但实际上，创建队列时并不能确定某队列是否已存在，如果用try的方式，像这样

try:
    channel.queue_declare(queue='rpc_queue')
except:
    channel.queue_delete(queue='rpc_queue')
    channel.queue_declare(queue='rpc_queue')

也会报错。报错信息：

Traceback (most recent call last):
  File "D:\rpc_server.py", line 11, in <module>
    channel.queue_declare(queue='rpc_queue')
  File "D:\liuzhibo\Python35\lib\site-packages\pika\adapters\blocking_connection.py", line 2329, in queue_declare
    self._flush_output(declare_ok_result.is_ready)
  File "D:\liuzhibo\Python35\lib\site-packages\pika\adapters\blocking_connection.py", line 1181, in _flush_output
    raise exceptions.ChannelClosed(method.reply_code, method.reply_text)
pika.exceptions.ChannelClosed: (406, "PRECONDITION_FAILED - inequivalent arg 'durable' for queue 'rpc_queue' in vhost '/': received 'false' but current is 'true'")

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "D:\rpc_server.py", line 13, in <module>
    channel.queue_delete(queue='rpc_queue')
  File "D:\liuzhibo\Python35\lib\site-packages\pika\adapters\blocking_connection.py", line 2351, in queue_delete
    nowait=False)
  File "D:\liuzhibo\Python35\lib\site-packages\pika\channel.py", line 717, in queue_delete
    self._validate_channel_and_callback(callback)
  File "D:\liuzhibo\Python35\lib\site-packages\pika\channel.py", line 1179, in _validate_channel_and_callback
    raise exceptions.ChannelClosed()
pika.exceptions.ChannelClosed

channel对象下貌似也没有判断一个队列是否存在的方法，那要怎么样动态的判断一个队列是否存在并删除之？

解决方案

错误很明显嘛，重新拿 channel 就好了：

# -*- coding: utf-8 -*-


import pika
import sys

connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()
channel.exchange_declare(exchange='first', type='fanout')


#channel.queue_declare(queue='hello')
#channel.queue_delete(queue='hello')
#sys.exit(0)

try:
    channel.queue_declare(queue='hello', durable=True)
except:
    channel = connection.channel()
    channel.queue_delete(queue='hello')
    channel.queue_declare(queue='hello', durable=True)


channel.queue_bind(exchange='first', queue='hello')
channel.basic_publish(exchange='first', routing_key='', body='Hello World!')

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