上篇文章中，我们构建了一个简单的日志系统。接下来，我们将丰富它：能够使用不同的severity来监听不同等级的log。比如我们希望只有error的log才保存到磁盘上。

1. Bindings绑定

    上篇文章中我们是这么做的绑定：

channel.queue_bind(exchange=exchange_name,
                   queue=queue_name)

    绑定其实就是关联了exchange和queue。或者这么说：queue对exchagne的内容感兴趣，exchange要把它的Message deliver到queue中。

    实际上，绑定可以带 routing_key 这个参数。其实这个参数的名称和 basic_publish 的参数名是相同了。为了避免混淆，我们把它成为binding key。
    使用一个key来创建binding :

channel.queue_bind(exchange=exchange_name,
                   queue=queue_name,
                   routing_key='black')

对于fanout的exchange来说，这个参数是被忽略的。

2. Direct exchange

  Direct exchange的路由算法非常简单：通过binding key的完全匹配，可以通过下图来说明。

3. Multiple bindings

  

4. Emitting logs

首先是我们要创建一个direct的exchange：

channel.exchange_declare(exchange='direct_logs',
                         type='direct')

我们将使用log的severity作为routing key，这样Consumer可以针对不同severity的log进行不同的处理。
publish：

channel.basic_publish(exchange='direct_logs',
                      routing_key=severity,
                      body=message)

我们使用三种severity：'info', 'warning', 'error'.

5. Subscribing

对于queue，我们需要绑定severity：

result = channel.queue_declare(exclusive=True)
queue_name = result.method.queue

for severity in severities:
    channel.queue_bind(exchange='direct_logs',
                       queue=queue_name,
                       routing_key=severity)

6. 最终版本

The code for emit_log_direct.py:

#!/usr/bin/env python
import pika
import sys

connection = pika.BlockingConnection(pika.ConnectionParameters(
        host='localhost'))
channel = connection.channel()

channel.exchange_declare(exchange='direct_logs',
                         type='direct')

severity = sys.argv[1] if len(sys.argv) > 1 else 'info'
message = ' '.join(sys.argv[2:]) or 'Hello World!'
channel.basic_publish(exchange='direct_logs',
                      routing_key=severity,
                      body=message)
print " [x] Sent %r:%r" % (severity, message)
connection.close()

The code for receive_logs_direct.py:

#!/usr/bin/env python
import pika
import sys

connection = pika.BlockingConnection(pika.ConnectionParameters(
        host='localhost'))
channel = connection.channel()

channel.exchange_declare(exchange='direct_logs',
                         type='direct')

result = channel.queue_declare(exclusive=True)
queue_name = result.method.queue

severities = sys.argv[1:]
if not severities:
    print >> sys.stderr, "Usage: %s [info] [warning] [error]" % \
                         (sys.argv[0],)
    sys.exit(1)

for severity in severities:
    channel.queue_bind(exchange='direct_logs',
                       queue=queue_name,
                       routing_key=severity)

print ' [*] Waiting for logs. To exit press CTRL+C'

def callback(ch, method, properties, body):
    print " [x] %r:%r" % (method.routing_key, body,)

channel.basic_consume(callback,
                      queue=queue_name,
                      no_ack=True)

channel.start_consuming()

我们想把warning和error的log记录到一个文件中：

$ python receive_logs_direct.py warning error > logs_from_rabbit.log

打印所有log到屏幕：

$ python receive_logs_direct.py info warning error
 [*] Waiting for logs. To exit press CTRL+C

尊重原创，转载请注明出处 anzhsoft: http://blog.csdn.net/anzhsoft/article/details/19630147

参考资料：

1. http://www.rabbitmq.com/tutorials/tutorial-four-python.html