title: How to add a header key:value pair when publishing a message with pika
body: <p>I am writing an automated test to test a consumer. So far I did not need to include a header when publishing messages but now I do. And it seems like its lacking documentation.</p>
  
  <p>This is my publisher:</p>
  
  <pre><code>class RMQProducer(object):
  
      def __init__(self, host, exchange, routing_key):
          self.host = host
          self.exchange = exchange
          self.routing_key = routing_key
  
      def publish_message(self, message):
          connection = pika.BlockingConnection(pika.ConnectionParameters(self.host))
          channel = connection.channel()
          message = json.dumps(message)
          channel.basic_publish(exchange=self.exchange,
                                routing_key=self.routing_key,
                                body=message)
  </code></pre>
  
  <p>I want to do smtn like:</p>
  
  <pre><code>channel.basic_publish(exchange=self.exchange,
                        routing_key=self.routing_key,
                        body=message,
                        headers={"key": "value"})
  </code></pre>
  
  <p>Whats the correct way to add headers to this message?</p>